The concept of co‐production suggests a collaborative production of public welfare services, across boundaries of participant categories, for example professionals, service users, peer‐workers and volunteers. While co‐production has been embraced in most European countries, the way in which it is translated into everyday practice remains understudied. Drawing on ethnographic data from Danish community mental health services, we attempt to fill this gap by critically investigating how participants interact in an organisational set‐up with blurred boundaries between participant categories. In particular, we clarify under what circumstances the blurred boundaries emerge as believable. Theoretically, we combine Lamont and Molnár's (2002) distinction between symbolic boundaries and social boundaries with Goffman's (1974) microanalysis of “principles of convincingness”. The article presents three findings: (1) co‐production is employed as a symbolic resource for blurring social boundaries; (2) the believability of blurred boundaries is worked up through participants’ access to resources of validation, knowledge and authority; and (3) incongruence between symbolic and social boundaries institutionalises practices where participants merely act ‘as if’ boundaries are blurred. Clarification of the principles of convincingness contributes to a general discussion of how co‐production frames the everyday negotiation of symbolic and social boundaries in public welfare services.