A conflict game simulating social traps in which a collective good can be provided by a volunteer is discussed and some solution concepts are analyzed. There is a greater incentive for “free riding” than for the production of the collective good at the cost of the volunteer. However, if everybody defects, all players will lose. Such a result is frequently produced by “diffusion of responsibility” as described by Darley and Latané (1968). In contrast to other social traps, a dominant strategy does not exist. Also, the mixed-equilibrium strategy yields very low payoffs. The expected gain is not greater than the payoff achieved by the nonequilibrium maximum strategy. Superrationality might be a way out of the trap. However, this concept lacks the desirable equilibrium property. Only in the free communication version of the game can a definitive answer to the question of a rational strategy be given.

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Theoretical propositions stressing the importance of trust, reciprocity, and reputation for cooperation in social exchange relations are deeply rooted in classical sociological thought. Today’s online markets provide a unique opportunity to test these theories using unobtrusive data. Our study investigates the mechanisms promoting cooperation in an online-auction market where most transactions can be conceived as one-time-only exchanges. We first give a systematic account of the theoretical arguments explaining the process of cooperative transactions. Then, using a large dataset comprising 14,627 mobile phone auctions and 339,517 DVD auctions, we test key hypotheses about the effects of traders’ reputations on auction outcomes and traders’ motives for leaving feedback. Our statistical analyses show that sellers with better reputations have higher sales and obtain higher prices. Furthermore, we observe a high rate of participation in the feedback system, which is largely consistent with strong reciprocity—a predisposition to unconditionally reward (or punish) one’s interaction partner’s cooperation (or defection)—and altruism—a predisposition to increase one’s own utility by elevating an interaction partner’s utility. Our study demonstrates how strong reciprocity and altruism can mitigate the free-rider problem in the feedback system to create reputational incentives for mutually beneficial online trade.

The low-cost hypothesis predicts that the strength of effects of environmental concern on environmental behavior diminishes with increasing behavioral costs. Thus, environmental concern in¯uences environmental behavior primarily in situations and under conditions connected with low costs and little inconvenience for individual actors. In a ®rst step, we develop and specify this hypothesis. Referring to two procedures, we then test it on the basis of an environmental survey of a random sample of 2307 respondents from the German population. The empirical evidence is positive. The lowcost hypothesis is not con®ned to the area of environmental research. It points to general limits of attitude-research (in highcost situations) and to general limits of rational-choice theory (in low-cost situations), and suggests a strategy for integrating research in social psychology, sociology, and economics. KEY WORDS . Attitudes and behavior . collective goods . environmental behaviour . low-cost hypothesis . rational choice . social norms Rationality and Society