PurposeResearch into the dark side of online brand-managed communities (OBCs) and, specifically, consumer-to-consumer (C2C) conflicts within this context are scarce. This paper aims to explore the different forms of C2C conflicts in OBCs, measure their direct impact on observing consumers and brands and investigate their appropriate moderation by exclusively focusing on two actors: brands versus consumers.Design/methodology/approachThis research adopts a sequential exploratory approach. First, the authors capture different forms of C2C conflict via netnographic observations of five brand-managed communities. Second, the identified forms of C2C conflict are used in an online experiment to examine their impact on OBCs’ social and commercial outcomes. Third, further two online experiments were used to assess how brand versus consumer conflict moderators impact perceived credibility and conflict de-escalation.FindingsThe authors uncover three prominent forms of C2C conflict based on whether conflict occurs between supporters, non-supporters or outsiders of the OBC. The authors further show that these affect consumers’ engagement behaviours and emotional responses, while brands suffer from diminished credibility and could be targets of unfavourable electronic word-of-mouth. Finally, for managing C2C conflict, the findings confirm that brands are perceived as more suitable, while under certain conditions consumers can also be viewed as appropriate moderators.Research limitations/implicationsThis research used a range of participant self-selected brands and is limited to brand-managed (as opposed to consumer-managed) communities on Facebook. While beyond the scope of this paper, the dynamics for consumer-managed communities may differ.Practical implicationsThis article offers guidance to marketing practitioners on the different nuances of undesirable consumer interactions in brand-managed communities on social media, their impact on customer engagement and brand perceptions and when/whether brands or consumers may be suited to moderating these.Originality/valueThis paper makes novel contributions to the literature on consumer (mis)behaviours and OBC management. The findings are among the first, to the best of the authors’ knowledge, to examine the direct social and commercial consequences of C2C conflicts and to provide comparative insights into the appropriateness of two different moderators in OBCs.