The strategy method is a powerful method for eliciting conditional cooperation in strategic interactions. Theoretically, players’ cooperation conditional on a specific level of others’ cooperation using the strategy method should be equal to their unconditional cooperation given an equivalent belief about others’ cooperation. However, using the Prisoner’s Dilemma, we show that decisions using the strategy method are more selfish than decisions under a simultaneous decision protocol predicted from players’ beliefs. This is driven entirely by lower cooperation among conditional cooperators with low expectations about others’ cooperation. We further show that relative to simultaneous choice, the strategy method shifts salient norms from an egalitarian fairness norm (‘give half’) to a reciprocity norm (‘match others’ behaviour’). This undermines cooperation among players with low beliefs about others’ cooperation. These results thus show that the strategy method does not merely hold beliefs constant, but also shifts which salient norms influence choice behaviour. This has important implications for the use of the strategy method in eliciting social preferences.