論eBay拍賣中購買價與底價的有無關係

eBay Online Auction with or without a Buy Price and a Reserve Price

Reynold and Wooders (2003) 分析eBay和Yahoo! Auctions的有購買價拍賣模式 中買方的均衡出價策略，但並未進一步探討購買價是如何決定的，也未提到底價的問題。本文以他們的單階段模型為基礎，針對eBay拍賣中附有購買價與底價的競價拍賣模式，建立一個三階段不完全信息的動態賽局模型。為簡化分析，模型中假定只有兩位潛在的買方，並且所有的參與者均為風險中立。根據本文的分析發現，給定賣方所設定的底價與購買價，存在著買方的均衡截斷策略組合，該策略組合之下的截斷價值的大小則與賣方所設定的底價與購買價有關。在拍賣品成本為零的假設之下，賣方最適的底價為零，其含義等同於不設定底價或將其設在成本的位置，至於購買價格的設定則非唯一，文中證明，不論賣方設定購買價與否都會得到唯一的賽局均衡結果。

This paper builds up a model of a sequential game with three stages and asymmetric information to analyze strategic interactions among players whom are involved in eBay online auction with or without a buy price and a reserve price. There are three players in the game, one seller and two potential buyers. All players are assumed to be risk neutral. In the first stage, the buyer posts an item for sale on eBay online auction, announcing its buy price and reserve price. After observing the buyer's action, the two potential buyers decide whether entering into the auction or not in the second stage. In the third stage, each player has to choose between bidding and using buy price. By the use of backward induction, this paper firstly deals with the issue of equilibrium strategy profile of the two potential buyers in the final stage. The seller's target is to choose a buy price and a reserve price to maximize her own payoffs given the equilibrium strategy profile of the buyers. It is shown that there is a u nique outcome even though there exist multiple equilibria for this game. To put it specifically, this paper argues that the equilibrium outcome will not be affected regardless of whether there are a buy price and a reserve price in auction, if all players are risk neutral.