Gah, just found a serious design flaw in multiplayer games that allows you to take money from others:
If you die completely with no clonks left and rejoin in the game, you'll respawn in a house thats very close to where your original house was placed. The flag atop your old house will turn to another player's color. You can take that flag and use it to buy things from houses without using your money, but the player whos color is of the flags, then hide it from them.
What is that? I just tested that out and its really really lame if your the person who's money is being stolen from.