Shill Bidding in English Auctions Wenli Wang Zoltan´ Hidvegi´ Andrew B. Whinston Decision and Information Analysis, Goizueta Business School, Emory University, Atlanta, GA, 30322 Center for Research on Electronic Commerce, Department of MSIS, The University of Texas at Austin, Austin, TX 78712 ¡ wenli
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[email protected] [email protected] First version: January, 2001 Current revision: September 6, 2001 Shill bidding in English auction is the deliberate placing bids on the seller’s behalf to artificially drive up the price of his auctioned item. Shill bidding has been known to occur in auctions of high-value items like art and antiques where bidders’ valuations differ and the seller’s payoff from fraud is high. We prove that private- value English auctions with shill bidding can result in a higher expected seller profit than first and second price sealed-bid auctions. To deter shill bidding, we introduce a mechanism which makes shill bidding unprofitable. The mechanism emphasizes the role of an auctioneer who charges the seller a commission fee based on the difference between the winning bid and the seller’s reserve. Commission rates vary from market to market and are mathematically determined to guarantee the non-profitability of shill bidding. We demonstrate through examples how this mechanism works and analyze the seller’s optimal strategy. The Internet provides auctions accessible to the general pub- erature on auction theories, which currently are insufficient to lic. Anyone can easily participate in online auctions, either as guide online practices. a seller or a buyer, and the value of items sold ranges from a One of the emerging issues is shill bidding, which has become few dollars to millions.