This article conceptualises how professionals, working according to customer involvement rationales in marketing contexts, experience and deal with the tension between their own identity, as regards having knowledge expertise, and the knowledge expertise they attribute to their customers. By relating the literature on professional identity to customer involvement in marketing, and by investigating this relationship in an empirical study of healthcare professionals influenced by customer involvement discourses, the article identifies the key underlying theoretical properties and mechanisms of professional reflexivity. A conceptual framework is outlined, displaying the key role of situated reflexivity by which means professionals enact ways of involving their customers, amidst a two-dimensional space defined by perceived professional and customer identities. It is argued that this conceptual framework details a social tension, between professionals and customers, that is highly visible in many service and marketing interactions and overlooked in marketing theory. It is argued that uncovering this tension adds to our understanding of why value is not always co-created in line with customer involvement rationales.