Auctions Tanzanites

Facts About Type of Auctions

English auction: This is what most people think of as an auction. Participants bid openly against one another, with each bid being higher than the previous bid. The auction ends when no participant is willing to bid further, or when a pre-determined "buy-out" price is reached, at which point the highest bidder pays the price. The seller may set a 'reserve' price and if the auctioneer fails to raise a bid higher than this reserve the sale may not go ahead.

Dutch auction: In the traditional Dutch auction the auctioneer begins with a high asking price which is lowered until some participant is willing to accept the auctioneer's price, or a predetermined minimum price is reached. That participant pays the last announced price. This type of auction is convenient when it is important to auction goods quickly, since a sale never requires more than one bid. The Dutch auction is named for its best known example, the Dutch tulip auctions; in the Netherlands this type of auction is actually known as a "Chinese auction". "Dutch auction" is also sometimes used to describe online auctions where several identical goods are sold simultaneously to an equal number of high bidders.

Sealed first-price auction: In this type of auction all bidders simultaneously submit bids in such a way that no bidder knows the bid of any other participant. The highest bidder pays the price he submitted.

Sealed second-price auction, also known as a Vickrey auction: This is identical to the sealed first-price auction, except the winning bidder pays the second highest bid rather than his own. Both the English and the second-price sealed-bid auctions will theoretically lead to the bidder's bidding up to (or submitting as a sealed bid) their true valuation of the item.

Silent auction: Often used in charity events. In this type of auction, items are displayed. Bidders can write a bid on a piece of paper located near the item. They may or may not know what the other people are bidding, which closes after a pre-set period of time. The highest bidder pays the price submitted.

Procurement auction: This kind of auction reverses the roles of seller and buyer. The buyer puts out an RFQ for a given commodity and providers offer progressively lower prices in hopes of getting the business. At the end of the auction, the lowest bid wins.
If more than one identical item is sold, there are two possible generalizations of the second-price auction. In a uniform-price auction, all of the winning bidders pay the price submitted by the highest non-winning bidder. Bidders will not typically bid their true value in a uniform-price auction with multiple units. In a Vickrey auction, the pricing rule is more complicated, but preserves the property that bidders will bid their true valuation. It is also possible to auction each identical item individually. Once each item has been priced, the winning bidder is entitled to buy the remaining goods at the same price. Items the winning bidder opts not to purchase are auctioned again. This system creates a tension between the desire to hold back on bidding since later items will almost certainly be cheaper, and the chance that by losing the first round of bidding all possibility of purchasing will be lost.

Bidders in the traditional Dutch auction and sealed first-price auction will tend to underbid what they believe the item is truly worth in hopes of getting the item for less, or in order to avoid the winner's curse. This behavior is known as bid shading. These two auctions are also theoretically equivalent, but in practice Dutch auctions will produce less revenue than sealed first-price auctions (one of the important results of Experimental economics)

Work in the theory of auctions contributed to Vickrey's 1996 Bank of Sweden Prize.