Go into Grab Mode, and select the object in your house that is worth the most money. For example, a flat screen TV. Then, tap it and tap the box button to put it into your Storage.

Exit Grab Mode and go into the Storage. Your TV is there. Tap on it so that it is green. Then tap on the gold, oval shaped button at the bottom of the screen. You should be in Grab Mode again, this time placing the TV. Don't touch anything. DO NOT place the TV anywhere. Just carefully tap the box on one of the tabs on the bottom bar on the screen.

You are back into your Storage. There will be the TV there again. Tap on it. Then tap on the red, oval shaped button at the bottom of the screen. There. You got the money from selling the object. But then, tap the back button and you will go back into placement mode... you will still be able to place the object you just sold! Tap anywhere in your house to place it, then tap on it again and press the box button to put it back into the Storage.

You can repeat this as often as you want.