Department of Mathematical Informatics, The University of Tokyo, Bunkyo, Tokyo, Japan.
PLoS One. 2012;7(9):e44169. doi: 10.1371/journal.pone.0044169. Epub 2012 Sep 7.
Many online marketplaces enjoy great success. Buyers and sellers in successful markets carry out cooperative transactions even if they do not know each other in advance and a moral hazard exists. An indispensable component that enables cooperation in such social dilemma situations is the reputation system. Under the reputation system, a buyer can avoid transacting with a seller with a bad reputation. A transaction in online marketplaces is better modeled by the trust game than other social dilemma games, including the donation game and the prisoner's dilemma. In addition, most individuals participate mostly as buyers or sellers; each individual does not play the two roles with equal probability. Although the reputation mechanism is known to be able to remove the moral hazard in games with asymmetric roles, competition between different strategies and population dynamics of such a game are not sufficiently understood. On the other hand, existing models of reputation-based cooperation, also known as indirect reciprocity, are based on the symmetric donation game. We analyze the trust game with two fixed roles, where trustees (i.e., sellers) but not investors (i.e., buyers) possess reputation scores. We study the equilibria and the replicator dynamics of the game. We show that the reputation mechanism enables cooperation between unacquainted buyers and sellers under fairly generous conditions, even when such a cooperative equilibrium coexists with an asocial equilibrium in which buyers do not buy and sellers cheat. In addition, we show that not many buyers may care about the seller's reputation under cooperative equilibrium. Buyers' trusting behavior and sellers' reputation-driven cooperative behavior coevolve to alleviate the social dilemma.
许多在线市场取得了巨大的成功。即使买家和卖家事先彼此不认识且存在道德风险，成功市场中的买卖双方也会进行合作交易。在这种社会困境情况下，合作的一个不可或缺的组成部分是声誉系统。在声誉系统中，买家可以避免与声誉不佳的卖家进行交易。与其他社会困境游戏（包括捐赠游戏和囚徒困境）相比，信任游戏更能很好地模拟在线市场中的交易。此外，大多数人主要作为买家或卖家参与其中；每个个体并非以相等的概率扮演这两个角色。虽然声誉机制被认为能够消除具有不对称角色的游戏中的道德风险，但对这种游戏中不同策略的竞争和群体动态的理解还不够充分。另一方面，基于声誉的合作的现有模型，也称为间接互惠，基于对称的捐赠游戏。我们分析了具有两个固定角色的信任游戏，其中受托人（即卖家）而不是投资者（即买家）拥有声誉评分。我们研究了该游戏的均衡和复制者动态。我们表明，在相当宽松的条件下，即使在这样的合作均衡与买家不购买且卖家欺诈的非社会均衡共存的情况下，声誉机制也能促进陌生买家和卖家之间的合作。此外，我们表明，在合作均衡下，可能没有多少买家关心卖家的声誉。买家的信任行为和卖家的声誉驱动的合作行为共同进化，以缓解社会困境。
