Three experiments investigated accuracy of discerning defectors from cooperators in one-shot prisoner's dilemma games. The prisoner's dilemma games were constructed in a manner that represented a typical social exchange situation. Overall, participants who were classmates and had known each other fairly well for the last few months failed to discern, better than chance, who cooperated and who defected in the prisoner's dilemma. Furthermore, it was shown that high-trusters were more accurate in cheater detection when the game was played anonymously, whereas those who were high in social anxiety were more accurate when the game was played between mutually identified players. The latter type of participants were also more accurate in judging the nature of interpersonal relations (who liked whom) in their class. Those findings were interpreted to represent two types of adaptive strategy for those who faces socially uncertain situations.