Bids as a Vehicle of (Mis)Information: Collusion in English Auctions with Affiliated Values

During an English auction, bidders' behaviour conveys information on their valuation of the prize. So whenever valuations are not independent, a bidder's strategy depends on the price at which his competitors drop out before he does. A ring of bidders can strategically manipulate the information reported through its members' bids, in order to mislead other bidders into bidding less aggressively and so allow a ring member to bid more aggressively. Collusion increases the probability that a ring bidder wins the auction and reduces the price he pays. The presence of a ring harms other bidders (as well as the seller) and reduces efficiency.