Auctions are particularly prone to fraud, which produces information asymmetries
between buyers and sellers. Some of the possible abuses and frauds include:
• Bid rigging: Agreeing offline to limit bids or using shills to submit false bids that
drive prices up.
• Price matching: Agreeing informally or formally to set floor prices on auction
items below which sellers will not sell in open markets.
• Shill feedback, defensive: Using secondary IDs or other auction members to
inflate seller ratings.
• Shill feedback, offensive: Using secondary IDs or other auction members to
deflate ratings for another user (feedback bombs).
• Feedback extortion: Threatening negative feedback in return for a benefit.
• Transaction interference: E-mailing buyers to warn them away from a seller.
• Bid manipulation: Using the retraction option to make high bids, discovering the
maximum bid of the current high bidder, and then retracting the bid.
• Non-payment after winning: Blocking legitimate buyers by bidding high, then not
paying.
• Shill bidding: Using secondary user IDs or other auction members to artificially
raise the price of an item.
• Transaction non-performance: Accepting payment and failing to deliver.
• Non-selling seller: Refusing payment or failing to deliver after a successful auction.