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Abstract of the journal article:
In 25 years, research on reputation-based online markets has produced robust evidence on the existence of the so-called reputation effect, i.e. the positive relation between online traders' reputations and these traders' market success in terms of sales and prices. However, there is an ongoing debate on what the size of the reputation effect means. We argue that the rate of truthful feedback that traders leave after completed transactions is negatively related to the size of the reputation effect. The higher the rate of truthful feedback, the quicker will untrustworthy traders be screened and disincentivized to enter the market. With mostly trustworthy traders entering the market, buyers will demand smaller price discounts from market entrants without a good reputation. We test this mechanism empirically in two laboratory experiments. In both experiments, we systematically vary the probability with which information about sellers' behavior in an economic trust game is recorded and shown to future interaction partners of these sellers. In the second experiment, we introduce competition among sellers by allowing buyers to choose one of two sellers in each interaction. We find that sellers give discounts to buyers to build or repair their reputation and that sellers who give discounts or have a good reputation are trusted more. However, we do not find support for our hypothesis that a higher feedback rate significantly decreases sellers' propensity to give discounts. We argue and show in exploratory analyses that this is likely due to the high level of unconditional trust buyers exhibit towards sellers without a reputation. Yet, seller competition increases the propensity to offer discounts among sellers without a reputation the most.

The tension between individual and collective interests and the provision of sanctioning mechanisms have been identified as important building blocks of a theory of norm emergence. Correspondingly, most investigations focus on how social norms emerge through explicit bargaining and social exchange to overcome this tension, and how sanctions enforce norm compliance. However, sanctioning presupposes the existence of the behavior at which it is directed, and the question of how behavior worth sanctioning can emerge tacitly if communication is not possible has hitherto received little attention. Here, we argue that game theory offers an ideal framework for theorizing about emergent behavioral regularities and show how latent norms can emerge from actors' recurring encounters in similar social dilemmas. We conduct two experiments in which small groups of subjects interact repeatedly in a volunteer's dilemma. We vary the heterogeneity of group members in terms of their costs of cooperation and the way they encounter each other in subsequent interactions. Our results show that subjects in homogeneous groups take turns at cooperating, whereas in heterogeneous groups mostly the subjects with the lowest costs cooperate. The emergence of solitary cooperation is moderated by the way subjects encounter each other again and their other-regarding preferences.

In the intertemporal common-pool resource game, non-cooperative behavior produces externalities reducing subjects' payoffs in both the present and the future. In this paper, we investigate through two experiments whether binding contracts, non-binding promises and social feedback help to promote sustainable behavior. We find that cooperation is higher in groups where a contract can be signed or where subjects made a promise to cooperate throughout the experiment. However, not all groups sign the contract unanimously and subjects who made a promise adjust their cooperation downwards over time. We find no difference between the control condition without any regulation and the treatment condition in which subjects receive feedback on their past behavior in private. However, if received feedback can be learned by all group members, cooperation is significantly higher. Our findings show that non-binding promises and social feedback increase cooperation, but the former only in the short-run and the latter only if made public.

Peer-punishment is an important determinant of cooperation in human groups. It has been suggested that, at the proximate level of analysis, punitive preferences can explain why humans incur costs to punish their deviant peers. How punitive preferences could have evolved in humans is still not entirely understood. A possible explanation at the ultimate level of analysis comes from signaling theory. It has been argued that the punishment of defectors can be a type-separating signal of the punisher's cooperative intent. As a result, punishers are selected more often as interaction partners in social exchange and are partly compensated for the costs they incur when punishing defectors. A similar argument has been made with regard to acts of generosity. In a laboratory experiment, we investigate whether the punishment of a selfish division of money in a dictator game is a sign of trustworthiness and whether punishers are more trustworthy interaction partners in a trust game than non-punishers. We distinguish between second-party and third-party punishment and compare punitive acts with acts of generosity as signs of trustworthiness. We find that punishers are not more trustworthy than non-punishers and that punishers are not trusted more than non-punishers, both in the second-party and in the third-party punishment condition. To the contrary, second-party punishers are trusted less than their non-punishing counterparts. However, participants who choose a generous division of money are more trustworthy and are trusted more than participants who choose a selfish division or participants about whom no information is available. Our results suggest that, unlike for punitive acts, the signaling benefits of generosity are to be gained in social exchange.

Peer-punishment is effective in promoting cooperation, but the costs associated with punishing defectors often exceed the benefits for the group. It has been argued that centralized punishment institutions can overcome the detrimental effects of peer-punishment. However, this argument presupposes the existence of a legitimate authority and leaves an unresolved gap in the transition from peer-punishment to centralized punishment. Here we show that the origins of centralized punishment could lie in individuals' distinct ability to punish defectors. In our laboratory experiment, we vary the structure of the punishment situation to disentangle the effects of punitive preferences, monetary incentives, and individual punishment costs on the punishment of defectors. We find that actors tacitly coordinate on the strongest group member to punish defectors, even if the strongest individual incurs a net loss from punishment. Such coordination leads to a more effective and more efficient provision of a cooperative environment than we observe in groups of all equals. Our results show that even an arbitrary assignment of an individual to a focal position in the social hierarchy can trigger the endogenous emergence of more centralized forms of punishment.

Social control and the enforcement of social norms glue a society together. It has been shown theoretically and empirically that informal punishment of wrongdoers fosters cooperation in human groups. Most of this research has focused on voluntary and uncoordinated punishment carried out by individual group members. However, as punishment is costly, it is an open question as to why humans engage in the punishment of wrongdoers even in one-time-only encounters. While evolved punitive preferences have been advocated as proximate explanations for such behaviour, the strategic nature of the punishment situation has remained underexplored. It has been suggested to conceive of the punishment situation as a volunteer's dilemma (VOD), where only one individual's action is necessary and sufficient to punish the wrongdoer. Here, we show experimentally that implementing the punishment situation as a VOD sustains cooperation in an environment where punishers and non-punishers coexist. Moreover, we show that punishment-cost heterogeneity allows individuals to tacitly agree on only the strongest group member carrying out the punishment, thereby increasing the effectiveness and efficiency of social norm enforcement. Our results corroborate that costly peer punishment can be explained without assuming punitive preferences and show that centralized sanctioning institutions can emerge from arbitrary individual differences.

It has been shown that psychological predispositions to benefit others can motivate human cooperation and the evolution of such social preferences can be explained with kin or multi-level selection models. It has also been shown that cooperation can evolve as a costly signal of an unobservable quality that makes a person more attractive with regard to other types of social interactions. Here we show that if a proportion of individuals with social preferences is maintained in the population through kin or multi-level selection, cooperative acts that are truly altruistic can be a costly signal of social preferences and make altruistic individuals more trustworthy interaction partners in social exchange. In a computerized laboratory experiment, we test whether altruistic behavior in the form of charitable giving is indeed correlated with trustworthiness and whether a charitable donation increases the observing agents' trust in the donor. Our results support these hypotheses and show that, apart from trust, responses to altruistic acts can have a rewarding or outcome-equalizing purpose. Our findings corroborate that the signaling benefits of altruistic acts that accrue in social exchange can ease the conditions for the evolution of social preferences.

Well-enforced norms create an opportunity for norm breakers to cooperate in ventures requiring trust. This is realized when norm breakers, by sharing evidence of their breaches, make themselves vulnerable to denunciation and therefore trustworthy. The sharing of compromising information (SCI) is a strategy employed by criminals, politicians, and other actors wary of their partners' trustworthiness in which the cost of ensuring compliance is offloaded on clueless norm enforcers. Here we introduce SCI as a sui generis cooperative strategy and test its functioning experimentally. In our experiment, subjects first acquire the label "dove" or "hawk" depending on how cooperative or uncooperative they are, respectively. Hawks acquire compromising information embodied in their label and can reveal it before an interaction with trust at stake. Unlike doves, hawks who reveal their label make themselves vulnerable to their partners, who can inflict a penalty on them after interaction. We find that even students in as artificial a setting as a computerized decision laboratory grasp the advantage of SCI and use it to cooperate. Our results corroborate the idea that compromising information can be conceived as a "hostage" that, when mutually exchanged, makes each party to the interaction vulnerable and therefore trustworthy in joint endeavours.