-Get a friendship with a rich Sim (girl recommended), then ask them to move in. The Sim will bring at least 20,000 Simoleons with them. The money will be added in your account. Then, you can make him or her move out.
-Enable the boolProp testingCheatsEnabled true code and hold SHIFT while clicking your mailbox, then select the "Force Robbery" option. Build a wall next to where the robber would appear and add burglar alarms all over it. Wait, and when the robber arrives, he will be caught. You will get a reward money from the police.