In light of the ongoing debate about the effectiveness of partial and impartial mediators, we examine how the Venezuelan government’s and the opposition’s perceptions of UNASUR and its good offices influenced its role as facilitator of dialogue between the two parties. We do so on the basis of interviews with key actors linked to the process, as well as a review of the literature and documentary sources. We find that, although there was a perception of lack of neutrality on the part of the mediators involved in the UNASUR effort to facilitate a dialogue in Venezuela, the parties themselves accepted the role of these mediators because they perceived that, through their means, they could achieve beneficial outcomes. Hence, we agree with various authors that the parties’ perception of a mediator is key. Nonetheless, we make a distinction between two types of perceptions that correspond to two types of legitimacy that a mediator can enjoy: ideological legitimacy and pragmatic legitimacy. We argue that the second type is essential and can explain the significant role that biased mediators play in various conflicts, such as that in Venezuela.