Some people worry about penny auction scams, but the biggest "scam" to watch out
for is simply to make sure you don't spend too much money on bids.
Bidders who bid but don't win have still spent money on their bids, so they frequently end up with nothing to show for their efforts. At least one website offers losing bidders the opportunity to buy merchandise making use of the value of their already-placed bids towards the price of the item in question. This gives even the "losers" something of value.