Assuming that social norms are engaged in all human-human interactions in an automatic manner, how to program a robot as to activate respect of social norms from humans? We argue that endowment effect, constituting a bias in decision making, could be produced by a “politeness effect” within the exchange paradigm of Knetsch (1989). To test this hypothesis, NAO, a humanoid robot took the place of the human experimenter and was programmed to behave in a neutral way, annihilating all non-verbal social cues emission. In this condition, politeness rules had been respected by minority in contrast with the same methodology lead by a human. Following this experiment, NAO was programmed as to re-activate social norms, using several non-verbal social cues: face tracking, intonations of voice and gestures. First results in this way tend to show the impact of non-verbal social cues, producing an endowment effect again.