Enable the "Free mode" code, then go to your house and buy a lot of expensive items. After that, save then restart your system. Do not enter the code again, then sell your items back for more money. The best item to do this with is the Monkey Butler Tree, which is worth 15,000 Simoleans. Make a wall parallel to the sidewalk (with the trash can and mail box). Put the most expensive wallpaper on both sides. Then, press Square to sell the wallpaper on one side. If this does not work, try the opposite side. You should be able to sell one side's wallpaper repeatedly.