In a common-value auction, every bidder is estimating the same unknown true value of the item, so the bidder whose estimate happens to be highest wins most often, and that winning estimate is, on average, an overestimate; economists call this the winner's curse. In a private-value auction, by contrast, each bidder assigns the item her own personal value rather than estimating a shared true value. A rare-coin dealer found that in her firm's common-value coin auctions, winning bids exceeded the coin's later-appraised value in most cases, but in her private-value estate-jewelry auctions, winning bids matched or fell below later appraisals just as often as they exceeded them.