Bukkit

From a player report:

"requires two people. one person (A) is the buyer. the other person (B) is the manipulater. person "A" first needs to NOT have enough money for the item they want to buy. person "B" needs to have enough. Person "A" goes to the shop and selects the item they want to buy and it should say "not enough money." after that, person "B" gets on and selects the same item (or a different one. as long as person "B" can afford it.) when selected, the sell screen for person "A" will change to item person "B" is buying. Person "A" clicks "buy" and will not spend any money on the item and person "B" just needs to watch the item. when person "A" buys it. person "B" will now no longer have the option to buy option. to fix this, both players should leave the shop and repeat the process again to continuously get free stuff."