diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5aa0bb0..aab6d76 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.8)
 
-project(kima2 VERSION 1.5.0)
+project(kima2 VERSION 1.4.2)
 
 set(CMAKE_MODULE_PATH "${CMAKE_HOME_DIRECTORY}/cmake")
 
@@ -12,8 +12,7 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 if(MSVC)
   add_compile_options(/W4 /WX)
 else()
-  #add_compile_options(-Wall -Wextra -pedantic -Woverloaded-virtual -Wredundant-decls -Wshadow)
-  add_compile_options(-Wall -Wextra)
+  add_compile_options(-Wall -Wextra -pedantic -Woverloaded-virtual -Wredundant-decls -Wshadow)
 endif()
 
 configure_file(config.h.in ${PROJECT_BINARY_DIR}/config.h)
@@ -31,11 +30,11 @@ endif()
 add_subdirectory(3rdparty)
 add_subdirectory(src)
 
-#if(NOT CMAKE_BUILD_TYPE OR CMAKE_BUILD_TYPE MATCHES Debug)
-#  include(CTest)
-#  enable_testing()
-#  add_subdirectory(test)
-#endif()
+if(NOT CMAKE_BUILD_TYPE OR CMAKE_BUILD_TYPE MATCHES Debug)
+  include(CTest)
+  enable_testing()
+  add_subdirectory(test)
+endif()
 
 
 # CPack
diff --git a/manual/Benutzerhandbuch.odt b/manual/Benutzerhandbuch.odt
index cb1354e..ab245ce 100644
Binary files a/manual/Benutzerhandbuch.odt and b/manual/Benutzerhandbuch.odt differ
diff --git a/manual/Benutzerhandbuch.pdf b/manual/Benutzerhandbuch.pdf
index 86442af..e4966fc 100644
Binary files a/manual/Benutzerhandbuch.pdf and b/manual/Benutzerhandbuch.pdf differ
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 504d0c3..3d9fa92 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -13,8 +13,6 @@ endif (MINGW)
 set(CORE_SOURCES
     database.cpp
     entity.cpp
-    entityint.cpp
-    entityuuid.cpp
     seller.cpp
     article.cpp
     sale.cpp
diff --git a/src/core/article.h b/src/core/article.h
index 50c0a9d..a497242 100644
--- a/src/core/article.h
+++ b/src/core/article.h
@@ -1,7 +1,7 @@
 #ifndef ARTICLE_H
 #define ARTICLE_H
 
-#include "entityuuid.h"
+#include "entity.h"
 //#include "sale.h"
 //#include "seller.h"
 
@@ -11,7 +11,7 @@
 class Seller;
 class Sale;
 
-class Article : public EntityUuid
+class Article : public Entity
 {
   public:
     Article() = default;
@@ -41,4 +41,4 @@ class Article : public EntityUuid
     std::string description_{};
 };
 
-#endif
+#endif
\ No newline at end of file
diff --git a/src/core/csvreader.cpp b/src/core/csvreader.cpp
index 73f95e1..ea0eea4 100644
--- a/src/core/csvreader.cpp
+++ b/src/core/csvreader.cpp
@@ -40,6 +40,7 @@ std::size_t CsvReader::readSellersFromFile(const fs::path& filePath, Marketplace
         }
 
         auto seller = std::make_unique<Seller>();
+        seller->createUuid();
         seller->setSellerNo(row[0].get<int>());
         if (row[1].is_int()) {
             seller->setNumArticlesOffered(row[1].get<int>());
@@ -55,9 +56,10 @@ std::size_t CsvReader::readSellersFromFile(const fs::path& filePath, Marketplace
     }
 
     // If there was no special seller "Sonderkonto" in import data, then create one
-    auto specialSeller = market->findSellerWithSellerNo(0);
+    auto specialSeller = market->findSellerWithUuid("11111111-1111-1111-1111-111111111111");
     if (!specialSeller) {
         auto seller = std::make_unique<Seller>();
+        seller->setUuidFromString("11111111-1111-1111-1111-111111111111");
         seller->setSellerNo(0);
         seller->setLastName("Sonderkonto");
         seller->setFirstName("Sonderkonto");
diff --git a/src/core/database.cpp b/src/core/database.cpp
index f95deae..123c467 100644
--- a/src/core/database.cpp
+++ b/src/core/database.cpp
@@ -75,10 +75,11 @@ void Database::createNew()
 
     std::string sqlCreateKima2{"CREATE TABLE IF NOT EXISTS kima2 ("
                                "version INTEGER NOT NULL);"
-                               "INSERT INTO kima2 (version) VALUES (3);"};
+                               "INSERT INTO kima2 (version) VALUES (2);"};
     sqlStrings.push_back(sqlCreateKima2);
     std::string sqlCreateSellers{"CREATE TABLE IF NOT EXISTS sellers ("
-                                 "seller_no INTEGER PRIMARY KEY NOT NULL, "
+                                 "id TEXT PRIMARY KEY NOT NULL, "
+                                 "seller_no INTEGER, "
                                  "first_name TEXT, "
                                  "last_name TEXT, "
                                  "num_offered_articles INTEGER, "
@@ -88,13 +89,13 @@ void Database::createNew()
     std::string sqlCreateArticles{
         "CREATE TABLE IF NOT EXISTS articles ("
         "id TEXT PRIMARY KEY NOT NULL, "
-        "seller_no TEXT NOT NULL, "
+        "seller_id TEXT NOT NULL, "
         "source_no INTEGER NOT NULL, "
         "article_no INTEGER NOT NULL, "
         "description TEXT, "
         "price INTEGER NOT NULL, "
         "UNIQUE (source_no, article_no), "
-        "FOREIGN KEY (seller_no) REFERENCES sellers(seller_no) ON DELETE CASCADE, "
+        "FOREIGN KEY (seller_id) REFERENCES sellers(id) ON DELETE CASCADE, "
         "CHECK (article_no BETWEEN 0 AND 99999)"
         ");"};
     sqlStrings.push_back(sqlCreateArticles);
@@ -114,9 +115,9 @@ void Database::createNew()
     sqlStrings.push_back(sqlCreateSalesItems);
 
     std::string sqlInitialEntries{
-        "INSERT OR IGNORE INTO sellers (seller_no, first_name, last_name, "
+        "INSERT OR IGNORE INTO sellers (id, seller_no, first_name, last_name, "
         "num_offered_articles) VALUES "
-        "(0, 'Sonderkonto', 'Sonderkonto', 0)"};
+        "('11111111-1111-1111-1111-111111111111', 0, 'Sonderkonto', 'Sonderkonto', 0)"};
     sqlStrings.push_back(sqlInitialEntries);
 
     beginTransaction();
@@ -129,18 +130,13 @@ void Database::createNew()
 void Database::updateDbToVer2()
 {
     beginTransaction();
-    exec("INSERT OR IGNORE INTO sellers (seller_no, first_name, last_name, "
+    exec("INSERT OR IGNORE INTO sellers (id, seller_no, first_name, last_name, "
          "num_offered_articles) VALUES "
-         "(0, 'Sonderkonto', 'Sonderkonto', 0)");
-    exec("UPDATE kima2 SET version = 3");
+         "('11111111-1111-1111-1111-111111111111', 0, 'Sonderkonto', 'Sonderkonto', 0)");
+    exec("UPDATE kima2 SET version = 2");
     endTransaction();
 }
 
-void Database::updateDbToVer3()
-{
-    newDb();
-}
-
 void Database::init()
 {
     const int errCode = sqlite3_open(dbname_.c_str(), &db_);
@@ -156,19 +152,12 @@ void Database::init()
     switch (version) {
     case 0:
         createNew();
-        initResult_ = InitResult::OK;
         break;
     case 1:
-        updateDbToVer3();
-        initResult_ = InitResult::OUTDATED_REPLACED;
-        break;
-    case 2:
-        updateDbToVer3();
-        initResult_ = InitResult::OUTDATED_REPLACED;
+        updateDbToVer2();
         break;
     default:
         // Do nothing because we are up-to-date.
-        initResult_ = InitResult::OK;
         break;
     }
 }
@@ -236,13 +225,16 @@ unsigned int Database::storeSellers(std::vector<std::unique_ptr<Seller>>& seller
             retCode = sqlite3_prepare_v2(
                 db_,
                 "INSERT INTO sellers"
-                " (seller_no, first_name, last_name, num_offered_articles)"
-                " VALUES (:seller_no, :first_name, :last_name, :num_offered_articles)",
+                " (id, seller_no, first_name, last_name, num_offered_articles)"
+                " VALUES (:uuid, :seller_no, :first_name, :last_name, :num_offered_articles)",
                 -1, &stmt, nullptr);
 
             if (retCode != SQLITE_OK)
                 throw std::runtime_error(sqlite3_errmsg(db_));
 
+            sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":uuid"),
+                              boost::uuids::to_string(seller->getUuid()).c_str(), -1,
+                              SQLITE_TRANSIENT);
             sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":seller_no"),
                              seller->getSellerNo());
             sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":first_name"),
@@ -268,14 +260,15 @@ unsigned int Database::storeSellers(std::vector<std::unique_ptr<Seller>>& seller
                 "UPDATE sellers SET"
                 " seller_no = :seller_no, first_name = :first_name,"
                 " last_name = :last_name, num_offered_articles = :num_offered_articles"
-                " WHERE seller_no = :id",
+                " WHERE id = :uuid",
                 -1, &stmt, nullptr);
 
             if (retCode != SQLITE_OK)
                 throw std::runtime_error(sqlite3_errmsg(db_));
 
-            sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":id"),
-                              seller->getId());
+            sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":uuid"),
+                              boost::uuids::to_string(seller->getUuid()).c_str(), -1,
+                              SQLITE_TRANSIENT);
             sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":seller_no"),
                              seller->getSellerNo());
             sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":first_name"),
@@ -299,13 +292,14 @@ unsigned int Database::storeSellers(std::vector<std::unique_ptr<Seller>>& seller
             count += static_cast<int>(seller->getArticles(false).size());
 
             retCode =
-                sqlite3_prepare_v2(db_, "DELETE FROM sellers WHERE seller_no = :id", -1, &stmt, nullptr);
+                sqlite3_prepare_v2(db_, "DELETE FROM sellers WHERE id = :uuid", -1, &stmt, nullptr);
 
             if (retCode != SQLITE_OK)
                 throw std::runtime_error(sqlite3_errmsg(db_));
 
-            sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":id"),
-                              seller->getId());
+            sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":uuid"),
+                              boost::uuids::to_string(seller->getUuid()).c_str(), -1,
+                              SQLITE_TRANSIENT);
 
             retCode = sqlite3_step(stmt);
 
@@ -352,7 +346,7 @@ unsigned int Database::storeArticles(std::vector<Article*> articles)
             retCode = sqlite3_prepare_v2(
                 db_,
                 "INSERT INTO articles"
-                " (id, seller_no, source_no, article_no, description, price)"
+                " (id, seller_id, source_no, article_no, description, price)"
                 " VALUES (:uuid, :seller_id, :source_no, :article_no, :desc, :price)",
                 -1, &stmt, nullptr);
 
@@ -362,8 +356,9 @@ unsigned int Database::storeArticles(std::vector<Article*> articles)
             sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":uuid"),
                               boost::uuids::to_string(article->getUuid()).c_str(), -1,
                               SQLITE_TRANSIENT);
-            sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":seller_id"),
-                              article->getSeller()->getId());
+            sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":seller_id"),
+                              boost::uuids::to_string(article->getSeller()->getUuid()).c_str(), -1,
+                              SQLITE_TRANSIENT);
             sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":source_no"),
                              article->getSourceNo());
             sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":article_no"),
@@ -387,7 +382,7 @@ unsigned int Database::storeArticles(std::vector<Article*> articles)
             retCode = sqlite3_prepare_v2(
                 db_,
                 "UPDATE articles SET"
-                " seller_no = :seller_id, source_no = :source_no, article_no = :article_no,"
+                " seller_id = seller_id, source_no = :source_no, article_no = :article_no,"
                 " description = :desc, price = :price"
                 " WHERE id = :uuid",
                 -1, &stmt, nullptr);
@@ -398,8 +393,9 @@ unsigned int Database::storeArticles(std::vector<Article*> articles)
             sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":uuid"),
                               boost::uuids::to_string(article->getUuid()).c_str(), -1,
                               SQLITE_TRANSIENT);
-            sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":seller_id"),
-                              article->getSeller()->getId());
+            sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":seller_id"),
+                              boost::uuids::to_string(article->getSeller()->getUuid()).c_str(), -1,
+                              SQLITE_TRANSIENT);
             sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":source_no"),
                              article->getSourceNo());
             sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":article_no"),
@@ -557,7 +553,7 @@ unsigned int Database::loadSellers(std::vector<std::unique_ptr<Seller>>& sellers
     sqlite3_stmt* stmt;
 
     retCode = sqlite3_prepare_v2(db_,
-                                 "SELECT seller_no, first_name, last_name, "
+                                 "SELECT id, seller_no, first_name, last_name, "
                                  "num_offered_articles FROM sellers ORDER BY seller_no",
                                  -1, &stmt, nullptr);
     if (retCode != SQLITE_OK)
@@ -570,10 +566,11 @@ unsigned int Database::loadSellers(std::vector<std::unique_ptr<Seller>>& sellers
     while (retCode != SQLITE_DONE) {
         ++count;
         auto seller = std::make_unique<Seller>();
-        seller->setSellerNo(sqlite3_column_int(stmt, 0));
-        seller->setFirstName(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 1)));
-        seller->setLastName(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 2)));
-        seller->setNumArticlesOffered(sqlite3_column_int(stmt, 3));
+        seller->setUuidFromString(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 0)));
+        seller->setSellerNo(sqlite3_column_int(stmt, 1));
+        seller->setFirstName(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 2)));
+        seller->setLastName(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 3)));
+        seller->setNumArticlesOffered(sqlite3_column_int(stmt, 4));
         seller->setState(Seller::State::OK);
         sellers.push_back(std::move(seller));
 
@@ -586,14 +583,14 @@ unsigned int Database::loadSellers(std::vector<std::unique_ptr<Seller>>& sellers
         retCode = sqlite3_prepare_v2(db_,
                                      "SELECT id, source_no, article_no, description, price"
                                      " FROM articles"
-                                     " WHERE seller_no = :seller_id"
+                                     " WHERE seller_id = :seller_uuid"
                                      " ORDER BY article_no",
                                      -1, &stmt, nullptr);
         if (retCode != SQLITE_OK)
             throw std::runtime_error(sqlite3_errmsg(db_));
 
-        sqlite3_bind_int(stmt, sqlite3_bind_parameter_index(stmt, ":seller_id"),
-                          seller->getId());
+        sqlite3_bind_text(stmt, sqlite3_bind_parameter_index(stmt, ":seller_uuid"),
+                          boost::uuids::to_string(seller->getUuid()).c_str(), -1, SQLITE_TRANSIENT);
 
         retCode = sqlite3_step(stmt);
 
@@ -749,4 +746,4 @@ void Database::updateCashPointNo(int oldCashPointNo, int newCashPointNo)
     sqlite3_finalize(stmt);
 
     endTransaction();
-}
+}
\ No newline at end of file
diff --git a/src/core/database.h b/src/core/database.h
index 2cf1b63..661d433 100644
--- a/src/core/database.h
+++ b/src/core/database.h
@@ -11,7 +11,6 @@
 class Database
 {
   public:
-    enum class InitResult {OK, OUTDATED_REPLACED};
     explicit Database(const std::string& dbname);
     Database();
     ~Database();
@@ -26,7 +25,6 @@ class Database
                            std::vector<std::unique_ptr<Seller>>& sellers);
     void updateCashPointNo(int oldCashPointNo, int newCashPointNo);
     void newDb();
-    InitResult getInitResult() {return initResult_;}
 
   private:
     sqlite3* db_{nullptr};
@@ -38,8 +36,6 @@ class Database
     int getVersion();
     unsigned int storeArticles(std::vector<Article*> articles);
     void updateDbToVer2();
-    void updateDbToVer3();
-    InitResult initResult_{InitResult::OK};
 };
 
-#endif // DATABASE_H
+#endif // DATABASE_H
\ No newline at end of file
diff --git a/src/core/entity.cpp b/src/core/entity.cpp
index 4a8cfb4..8caa834 100644
--- a/src/core/entity.cpp
+++ b/src/core/entity.cpp
@@ -1,6 +1,33 @@
 #include "entity.h"
 
+#include <iostream>
+
+#include <boost/uuid/uuid_generators.hpp>
+#include <boost/uuid/uuid_io.hpp>
+
+Entity::~Entity() = default;
+
+void Entity::createUuid()
+{
+    static boost::uuids::random_generator generator{};
+    uuid_ = generator();
+}
+
+void Entity::setUuidFromString(const std::string& uuidString)
+{
+    boost::uuids::string_generator generator{};
+    uuid_ = generator(uuidString);
+}
+
 Entity::State Entity::getState() const
 {
     return state_;
 }
+
+void Entity::setSourceNo(int sourceNo) {
+    sourceNo_ = sourceNo;
+}
+
+int Entity::getSourceNo() const {
+    return sourceNo_;
+}
\ No newline at end of file
diff --git a/src/core/entity.h b/src/core/entity.h
index 68b3ba7..017b6e0 100644
--- a/src/core/entity.h
+++ b/src/core/entity.h
@@ -1,16 +1,35 @@
 #ifndef ENTITY_H
 #define ENTITY_H
 
+#include <string>
+
+#include <boost/uuid/uuid.hpp>
+#include <boost/uuid/uuid_io.hpp>
+
 class Entity
 {
-public:
+  public:
     enum class State { NEW, UPDATE, DELETE, OK };
-    //virtual ~Entity() = 0;
-    void setState(State state) { state_ = state; }
-    virtual State getState() const;
 
-private:
+    // Entity() = default;
+    virtual ~Entity() = 0;
+
+    void createUuid();
+    void setUuidFromString(const std::string& uuidString);
+    void setState(State state) { state_ = state; }
+    void setSourceNo(int sourceNo);
+
+    const boost::uuids::uuid& getUuid() const { return uuid_; };
+    std::string getUuidAsString() const { return boost::uuids::to_string(uuid_); }
+    virtual State getState() const;
+    virtual int getSourceNo() const;
+
+  protected:
+    int sourceNo_{};
+
+  private:
+    boost::uuids::uuid uuid_{};
     State state_{State::NEW};
 };
 
-#endif // ENTITY_H
+#endif // ENTITY_H
\ No newline at end of file
diff --git a/src/core/entityint.cpp b/src/core/entityint.cpp
deleted file mode 100644
index 835c5ff..0000000
--- a/src/core/entityint.cpp
+++ /dev/null
@@ -1,9 +0,0 @@
-#include "entityint.h"
-
-EntityInt::EntityInt(int id) {
-    id_ = id;
-}
-
-void EntityInt::setId(int id) {
-    id_ = id;
-}
diff --git a/src/core/entityint.h b/src/core/entityint.h
deleted file mode 100644
index 9430a70..0000000
--- a/src/core/entityint.h
+++ /dev/null
@@ -1,18 +0,0 @@
-#ifndef ENTITY_INT_H
-#define ENTITY_INT_H
-
-#include "entity.h"
-
-class EntityInt : public Entity
-{
-  public:
-    EntityInt() = default;
-    EntityInt(int id);
-    void setId(int id);
-    int getId() const { return id_; };
-
-  protected:
-    int id_{};
-};
-
-#endif // ENTITY_INT_H
diff --git a/src/core/entityuuid.cpp b/src/core/entityuuid.cpp
deleted file mode 100644
index 4ec15ab..0000000
--- a/src/core/entityuuid.cpp
+++ /dev/null
@@ -1,29 +0,0 @@
-#include "entityuuid.h"
-
-#include <iostream>
-
-#include <boost/uuid/uuid_generators.hpp>
-#include <boost/uuid/uuid_io.hpp>
-
-EntityUuid::~EntityUuid() = default;
-
-void EntityUuid::createUuid()
-{
-    static boost::uuids::random_generator generator{};
-    uuid_ = generator();
-}
-
-void EntityUuid::setUuidFromString(const std::string& uuidString)
-{
-    boost::uuids::string_generator generator{};
-    uuid_ = generator(uuidString);
-}
-
-
-void EntityUuid::setSourceNo(int sourceNo) {
-    sourceNo_ = sourceNo;
-}
-
-int EntityUuid::getSourceNo() const {
-    return sourceNo_;
-}
diff --git a/src/core/entityuuid.h b/src/core/entityuuid.h
deleted file mode 100644
index 9b99ba7..0000000
--- a/src/core/entityuuid.h
+++ /dev/null
@@ -1,32 +0,0 @@
-#ifndef ENTITY_UUID_H
-#define ENTITY_UUID_H
-
-#include "entity.h"
-
-#include <string>
-
-#include <boost/uuid/uuid.hpp>
-#include <boost/uuid/uuid_io.hpp>
-
-class EntityUuid : public Entity
-{
-  public:
-    // Entity() = default;
-    virtual ~EntityUuid() = 0;
-
-    void createUuid();
-    void setUuidFromString(const std::string& uuidString);
-    void setSourceNo(int sourceNo);
-
-    const boost::uuids::uuid& getUuid() const { return uuid_; };
-    std::string getUuidAsString() const { return boost::uuids::to_string(uuid_); }
-    virtual int getSourceNo() const;
-
-  protected:
-    int sourceNo_{};
-
-  private:
-    boost::uuids::uuid uuid_{};
-};
-
-#endif // ENTITY_UUID_H
diff --git a/src/core/excelreader.cpp b/src/core/excelreader.cpp
index 7ef401d..cd0a8d7 100644
--- a/src/core/excelreader.cpp
+++ b/src/core/excelreader.cpp
@@ -39,6 +39,7 @@ std::size_t ExcelReader::readSellersFromFile(const fs::path& filePath, Marketpla
             continue;
         }
         auto seller = std::make_unique<Seller>();
+        seller->createUuid();
         seller->setSellerNo(row[0].value<int>());
         seller->setNumArticlesOffered(row[1].value<int>());
         std::string firstName = row[2].value<std::string>();
@@ -50,9 +51,10 @@ std::size_t ExcelReader::readSellersFromFile(const fs::path& filePath, Marketpla
     }
 
     // If there was no special seller "Sonderkonto" in import data, then create one
-    auto specialSeller = market->findSellerWithSellerNo(0);
+    auto specialSeller = market->findSellerWithUuid("11111111-1111-1111-1111-111111111111");
     if (!specialSeller) {
         auto seller = std::make_unique<Seller>();
+        seller->setUuidFromString("11111111-1111-1111-1111-111111111111");
         seller->setSellerNo(0);
         seller->setLastName("Sonderkonto");
         seller->setFirstName("Sonderkonto");
diff --git a/src/core/jsonutil.cpp b/src/core/jsonutil.cpp
index 873bb7b..dddf79a 100644
--- a/src/core/jsonutil.cpp
+++ b/src/core/jsonutil.cpp
@@ -15,6 +15,7 @@ void JsonUtil::exportSellers(const std::filesystem::path& filePath, Marketplace*
 
     for (const auto& seller : market->getSellers()) {
         json newEntry;
+        newEntry["uuid"] = seller->getUuidAsString();
         newEntry["seller_no"] = seller->getSellerNo();
         newEntry["last_name"] = seller->getLastName();
         newEntry["first_name"] = seller->getFirstName();
@@ -37,6 +38,7 @@ void JsonUtil::importSellers(const std::filesystem::path& filePath, Marketplace*
 
     for (auto val : jsonValues["sellers"]) {
         auto seller = std::make_unique<Seller>();
+        seller->setUuidFromString(val["uuid"]);
         seller->setSellerNo(val["seller_no"]);
         seller->setLastName(val["last_name"]);
         seller->setFirstName(val["first_name"]);
@@ -45,9 +47,10 @@ void JsonUtil::importSellers(const std::filesystem::path& filePath, Marketplace*
     }
 
     // If there was no special seller "Sonderkonto" in import data, then create one
-    auto specialSeller = market->findSellerWithSellerNo(0);
+    auto specialSeller = market->findSellerWithUuid("11111111-1111-1111-1111-111111111111");
     if (!specialSeller) {
         auto seller = std::make_unique<Seller>();
+        seller->setUuidFromString("11111111-1111-1111-1111-111111111111");
         seller->setSellerNo(0);
         seller->setLastName("Sonderkonto");
         seller->setFirstName("Sonderkonto");
@@ -78,7 +81,7 @@ void JsonUtil::exportSales(const std::filesystem::path& filePath, Marketplace* m
         for (const auto& article : sale->getArticles()) {
             json newArticle;
             newArticle["uuid"] = article->getUuidAsString();
-            newArticle["seller_no"] = article->getSeller()->getSellerNo();
+            newArticle["seller_uuid"] = article->getSeller()->getUuidAsString();
             newArticle["desc"] = article->getDescription();
             newArticle["price"] = article->getPrice();
             // newArticle["source_no"] = article->getSourceNo();
@@ -119,7 +122,7 @@ void JsonUtil::importSales(const std::filesystem::path& filePath, Marketplace* m
             article->setArticleNo(valArticle["article_no"]);
             article->setDescription(valArticle["desc"]);
             article->setPrice(valArticle["price"]);
-            auto seller = market->findSellerWithSellerNo(valArticle["seller_no"]);
+            auto seller = market->findSellerWithUuid(valArticle["seller_uuid"]);
             if (seller == nullptr) {
                 throw std::runtime_error(
                     "Die zu importierenden Daten verweisen auf einen nicht vorhandenen Verkäufer. "
@@ -133,4 +136,4 @@ void JsonUtil::importSales(const std::filesystem::path& filePath, Marketplace* m
     }
 
     market->storeToDb();
-}
+}
\ No newline at end of file
diff --git a/src/core/marketplace.cpp b/src/core/marketplace.cpp
index c9f4b7a..8f666fe 100644
--- a/src/core/marketplace.cpp
+++ b/src/core/marketplace.cpp
@@ -13,9 +13,9 @@ namespace fs = std::filesystem;
 
 Marketplace::Marketplace()
 {
-    /*auto seller = std::make_unique<Seller>("Max", "Mustermann");
+    auto seller = std::make_unique<Seller>("Max", "Mustermann");
     seller->createUuid();
-    sellers_.push_back(std::move(seller)); */
+    sellers_.push_back(std::move(seller));
 }
 
 void Marketplace::storeToDb(bool onlyDelete)
@@ -25,12 +25,11 @@ void Marketplace::storeToDb(bool onlyDelete)
     db.storeSales(sales_);
 }
 
-Database::InitResult Marketplace::loadFromDb()
+void Marketplace::loadFromDb()
 {
     Database db;
     db.loadSellers(sellers_);
     db.loadSales(sales_, sellers_);
-    return db.getInitResult();
 }
 
 SellersVec& Marketplace::getSellers() { return sellers_; }
@@ -104,7 +103,6 @@ Seller* Marketplace::findSellerWithSellerNo(int sellerNo)
     return (*iter).get();
 }
 
-/*
 Seller* Marketplace::findSellerWithUuid(const std::string& uuid)
 {
     auto iter = std::find_if(sellers_.begin(), sellers_.end(),
@@ -113,7 +111,6 @@ Seller* Marketplace::findSellerWithUuid(const std::string& uuid)
         return nullptr;
     return (*iter).get();
 }
-*/
 
 void Marketplace::addArticleToBasket(std::unique_ptr<Article> article)
 {
@@ -292,4 +289,4 @@ void Marketplace::clear()
     Database db;
     db.newDb();
     loadFromDb();
-}
+}
\ No newline at end of file
diff --git a/src/core/marketplace.h b/src/core/marketplace.h
index 47e25bd..758f758 100644
--- a/src/core/marketplace.h
+++ b/src/core/marketplace.h
@@ -1,7 +1,6 @@
 #ifndef MARKETPLACE_H
 #define MARKETPLACE_H
 
-#include "database.h"
 #include "article.h"
 #include "sale.h"
 #include "seller.h"
@@ -24,7 +23,7 @@ class Marketplace
     Marketplace();
 
     void storeToDb(bool onlyDelete = false);
-    Database::InitResult loadFromDb();
+    void loadFromDb();
 
     SellersVec& getSellers();
     SalesVec& getSales();
@@ -70,4 +69,4 @@ std::string marketFeeAsString(int sumInCent, int percent, int maxFeeInCent);
 std::string paymentAsString(int sumInCent, int percent, int maxFeeInCent);
 std::string escapeCsvValue(const std::string& value, const char delimiter);
 
-#endif
+#endif
\ No newline at end of file
diff --git a/src/core/sale.h b/src/core/sale.h
index 0cfb18c..c6de317 100644
--- a/src/core/sale.h
+++ b/src/core/sale.h
@@ -14,7 +14,7 @@ namespace
 using ArticlesVec = std::vector<Article*>;
 }
 
-class Sale : public EntityUuid
+class Sale : public Entity
 {
   public:
     void addArticle(Article* articlePtr);
@@ -34,4 +34,4 @@ class Sale : public EntityUuid
     mutable ArticlesVec articles_{};
 };
 
-#endif
+#endif
\ No newline at end of file
diff --git a/src/core/seller.cpp b/src/core/seller.cpp
index cc053ce..9147934 100644
--- a/src/core/seller.cpp
+++ b/src/core/seller.cpp
@@ -7,14 +7,15 @@
 
 Seller::Seller(const std::string& firstName, const std::string& lastName, int sellerNo,
                int numArticlesOffered)
-    : EntityInt(sellerNo)
+    : Entity()
 {
     firstName_ = firstName;
     lastName_ = lastName;
+    sellerNo_ = sellerNo;
     numArticlesOffered_ = numArticlesOffered;
 }
 
-void Seller::setSellerNo(int seller_no) { setId(seller_no); }
+void Seller::setSellerNo(int seller_no) { sellerNo_ = seller_no; }
 
 void Seller::setFirstName(const std::string& firstName) { firstName_ = firstName; }
 
@@ -32,13 +33,13 @@ std::string Seller::getFirstName() const { return firstName_; }
 
 std::string Seller::getLastName() const { return lastName_; }
 
-int Seller::getSellerNo() const { return getId(); }
+int Seller::getSellerNo() const { return sellerNo_; }
 
 std::string Seller::getSellerNoAsString() const
 {
     std::stringstream selNoStr;
 
-    selNoStr << std::setfill('0') << std::setw(3) << id_;
+    selNoStr << std::setfill('0') << std::setw(3) << sellerNo_;
 
     return selNoStr.str();
     ;
@@ -103,8 +104,8 @@ int Seller::sumInCents()
 
 std::string Seller::sumAsString() { return formatCentAsEuroString(sumInCents()); }
 
-bool operator<(const Seller& li, const Seller& re) { return li.id_ < re.id_; }
+bool operator<(const Seller& li, const Seller& re) { return li.sellerNo_ < re.sellerNo_; }
 bool operator<(const std::unique_ptr<Seller>& li, const std::unique_ptr<Seller>& re)
 {
-    return li->id_ < re->id_;
-}
+    return li->sellerNo_ < re->sellerNo_;
+}
\ No newline at end of file
diff --git a/src/core/seller.h b/src/core/seller.h
index a4bfde1..db44a0f 100644
--- a/src/core/seller.h
+++ b/src/core/seller.h
@@ -2,7 +2,7 @@
 #define SELLER_H
 
 #include "article.h"
-#include "entityint.h"
+#include "entity.h"
 
 #include <memory>
 #include <string>
@@ -10,11 +10,11 @@
 
 // class Article;
 
-class Seller : public EntityInt
+class Seller : public Entity
 {
   public:
     Seller() = default;
-    ~Seller() = default;
+    // virtual ~Seller() = default;
     Seller(const std::string& firstName, const std::string& lastName, int sellerNo = 0,
            int numArticlesOffered = 0);
 
@@ -42,10 +42,11 @@ class Seller : public EntityInt
     friend bool operator<(const std::unique_ptr<Seller>& li, const std::unique_ptr<Seller>& re);
 
   private:
+    int sellerNo_{-1};
     int numArticlesOffered_{};
     std::string firstName_{};
     std::string lastName_{};
     std::vector<std::unique_ptr<Article>> articles_{};
 };
 
-#endif
+#endif
\ No newline at end of file
diff --git a/src/gui/mainwindow.cpp b/src/gui/mainwindow.cpp
index 4ce75db..678a5cf 100644
--- a/src/gui/mainwindow.cpp
+++ b/src/gui/mainwindow.cpp
@@ -35,13 +35,7 @@ MainWindow::MainWindow()
     ui_.setupUi(this);
 
     marketplace_ = std::make_unique<Marketplace>();
-    Database::InitResult res = marketplace_->loadFromDb();
-    if (res == Database::InitResult::OUTDATED_REPLACED) {
-        QMessageBox(QMessageBox::Icon::Information, "Datenbankinformation",
-                    "Es wurde eine <b>veraltete</b> Datenbankdatei erkannt.<br />Diese wurde "
-                    "umbenannt und eine <b>neue</b> Datei wurde erstellt.")
-            .exec();
-    }
+    marketplace_->loadFromDb();
     statusBar()->showMessage("Gespeicherte Daten wurden geladen.", STATUSBAR_TIMEOUT);
 
     BasketModel* model = new BasketModel(getMarketplace(), ui_.basketView);
@@ -455,6 +449,14 @@ void MainWindow::onImportSellerExcelActionTriggered()
         return;
     }
 
+    QMessageBox(
+        QMessageBox::Icon::Information, "Bitte beachten",
+        "<b>Achtung:</b> Importieren Sie die Verkäuferdaten nur auf <b>einer (!)</b> "
+        "KIMA2-Installation.<br /> "
+        "Verteilen Sie die Daten auf die anderen Installationen unbedingt über eine JSON-Datei!",
+        QMessageBox::StandardButton::Ok, this)
+        .exec();
+
     auto filename = QFileDialog::getOpenFileName(
         this, "Verkäufer importieren", QString(),
         "Alle unterstützte Dateien (*.xlsx *.csv);;Excel Dateien (*.xlsx);;CSV Dateien (*.csv)");
diff --git a/src/gui/reportdialog.cpp b/src/gui/reportdialog.cpp
index 9cb7393..3a84ec4 100644
--- a/src/gui/reportdialog.cpp
+++ b/src/gui/reportdialog.cpp
@@ -102,7 +102,7 @@ void ReportDialog::onPrintReportButtonClicked()
         for (unsigned int j = 0;
              j < ENTRIES_PER_PAGE && (i - 1) * ENTRIES_PER_PAGE + j < sellers.size(); ++j) {
             int idx = (i - 1) * ENTRIES_PER_PAGE + j;
-            if (sellers.at(idx)->getId() == 0) {
+            if (sellers.at(idx)->getUuidAsString() == "11111111-1111-1111-1111-111111111111") {
                 continue;
             }
             content += QString("%1 %2 %3 %4 %5 %6 %7\n")
@@ -121,7 +121,7 @@ void ReportDialog::onPrintReportButtonClicked()
     }
 
     // pieces booked on the special account "Sonderkonto"
-    const auto specialSeller = market_->findSellerWithSellerNo(0);
+    const auto specialSeller = market_->findSellerWithUuid("11111111-1111-1111-1111-111111111111");
     if (specialSeller && specialSeller->numArticlesSold() > 0) {
         printer.newPage();
         painter.setFont(QFont("Arial", 16, QFont::Bold));
diff --git a/src/gui/reportmodel.cpp b/src/gui/reportmodel.cpp
index 65d386f..888430b 100644
--- a/src/gui/reportmodel.cpp
+++ b/src/gui/reportmodel.cpp
@@ -59,7 +59,7 @@ QVariant ReportModel::data(const QModelIndex& index, int role) const
 
     switch (index.column()) {
     case 0:
-        return seller->getId();
+        return seller->getUuidAsString().c_str();
     case 1:
         return seller->getSellerNo();
     case 2:
@@ -104,4 +104,4 @@ QVariant ReportModel::headerData(int section, Qt::Orientation orientation, int r
         // return QStringLiteral("%1").arg(section);
     } else
         return "";
-}
+}
\ No newline at end of file
diff --git a/src/gui/salemodel.cpp b/src/gui/salemodel.cpp
index 3549003..0bf9a71 100644
--- a/src/gui/salemodel.cpp
+++ b/src/gui/salemodel.cpp
@@ -44,7 +44,7 @@ QModelIndex SaleModel::parent(const QModelIndex& index) const
     Sale* sale{};
     Article* article{};
 
-    EntityUuid* ent = static_cast<EntityUuid*>(index.internalPointer());
+    Entity* ent = static_cast<Entity*>(index.internalPointer());
 
     sale = dynamic_cast<Sale*>(ent);
 
diff --git a/src/gui/sellermodel.cpp b/src/gui/sellermodel.cpp
index 9b9e660..7ec2356 100644
--- a/src/gui/sellermodel.cpp
+++ b/src/gui/sellermodel.cpp
@@ -31,7 +31,7 @@ QVariant SellerModel::data(const QModelIndex& index, int role) const
      */
     switch (index.column()) {
     case 0:
-        return seller->getId();
+        return seller->getUuidAsString().c_str();
     case 1:
         return seller->getSellerNo();
     case 2:
@@ -85,7 +85,7 @@ bool SellerModel::setData(const QModelIndex& index, const QVariant& value, int r
 
     switch (index.column()) {
     case 0:
-        seller->setId(value.toInt());
+        seller->setUuidFromString(value.toString().toStdString());
         break;
     case 1: {
         if (value.toInt() < 0)
@@ -126,6 +126,7 @@ bool SellerModel::insertRows(int row, int count, const QModelIndex& parent)
 {
     emit beginInsertRows(parent, row, row + count - 1);
     auto seller = std::make_unique<Seller>();
+    seller->createUuid();
     seller->setSellerNo(marketplace_->getNextSellerNo());
     marketplace_->getSellers().push_back(std::move(seller));
     emit endInsertRows();
@@ -141,7 +142,7 @@ bool SellerModel::removeRows(int row, int count, const QModelIndex& parent)
         marketplace_->getSellers().erase(
             std::remove_if(marketplace_->getSellers().begin(), marketplace_->getSellers().end(),
                            [&seller](const std::unique_ptr<Seller>& a) {
-                               return a->getId() == seller->getId();
+                               return a->getUuid() == seller->getUuid();
                            }),
             marketplace_->getSellers().end());
         emit endRemoveRows();
@@ -155,4 +156,4 @@ bool SellerModel::removeRows(int row, int count, const QModelIndex& parent)
     }
 
     return false;
-}
+}
\ No newline at end of file
diff --git a/test/test_seller.cpp b/test/test_seller.cpp
index 7d07b5b..45a41d6 100644
--- a/test/test_seller.cpp
+++ b/test/test_seller.cpp
@@ -9,14 +9,14 @@
 BOOST_AUTO_TEST_CASE(create_uuid_nil)
 {
     Seller seller{};
-    BOOST_TEST(seller.getId().is_nil() == true);
+    BOOST_TEST(seller.getUuid().is_nil() == true);
 }
 
 BOOST_AUTO_TEST_CASE(create_uuid)
 {
     Seller seller{};
     seller.createUuid();
-    BOOST_TEST(seller.getId().is_nil() == false);
+    BOOST_TEST(seller.getUuid().is_nil() == false);
 }
 
 BOOST_AUTO_TEST_CASE(create_many)
@@ -25,7 +25,7 @@ BOOST_AUTO_TEST_CASE(create_many)
     std::array<Seller, QUANTITY> sellers;
     for (unsigned i = 0; i < sellers.size(); i++) {
         sellers[i] = Seller();
-        //sellers[i].createUuid();
+        sellers[i].createUuid();
     }
 }
 
@@ -37,4 +37,4 @@ BOOST_AUTO_TEST_CASE(with_article) {
     BOOST_TEST((article == nullptr));
     BOOST_TEST(seller.getArticles(false).at(0)->getDescription() == "Test article");
     BOOST_TEST(seller.numArticlesSold() == 0);
-}
+}
\ No newline at end of file