Using an economic bargaining game, we tested for the existence of two phenomena related to social norms, namely norm manipulation – the selection of an interpretation of the norm that best suits an individual – and norm evasion – the deliberate, private violation of a social norm. We found that the manipulation of a norm of fairness was characterized by a self-serving bias in beliefs about what constituted normatively acceptable behaviour, so that an individual who made an uneven bargaining offer not only genuinely believed it was fair, but also believed that recipients found it fair, even though recipients of the offer considered it to be unfair. In contrast, norm evasion operated as a highly explicit process. When they could do so without the recipient's knowledge, individuals made uneven offers despite knowing that their behaviour was unfair.