Warning: Do this at your own risk!

Earning money has never been easier:

1. Play the game until you can buy a couple shops. The more the merrier.

2. Save and quit. Then turn off your Xbox 360 and turn it back on.

3. Change the time and date, to say, a year from today.

4. Go back in the game and get your money :P.

5. Buy everything you want, more shops, bigger houses and repeat process.

Note: You can only turn time ahead by a maximum of one month at a time [thanks Skip2MJ]