Abstract The article scrutinizes the Dutch healthcare market system to provide empirical grounding to the debates around the extent to which rationally constructed markets can develop as originally planned. Focusing on one specific pricing device, we document how the perceived economic ‘rationalities’ embedded in its design are challenged by the unforeseen and unanticipated ‘irrationalities’ of daily practices. We trace how healthcare professionals developed informal ways to adapt to the rules and expectations embedded in that device, resulting in forms of ‘counter performativity’ that threaten the quality and accessibility of Dutch healthcare. The main theoretical contribution of the article is to bridge the gap between ‘Actor Network Theory-based economic sociology’ and its emphasis on (counter-) performativity and the agency of devices with the older European continental inflections building on Weber, Durkheim and Bourdieu, by drawing attention to the distinct epistemologies of different professions, using insights from James Scott and the sociology of the professions.