In many countries, general practitioners (GPs) are assigned the task of controlling the validity of their own patients' insurance claims. At the same time, they operate in a market where patients are customers free to choose their GP. Are these roles compatible? Can we trust that the gatekeeping decisions are untainted by private economic interests? Based on administrative registers from Norway with records on sick pay certification and GP-patient relationships, we present evidence to the contrary: GPs are more lenient gatekeepers the more competitive is the physician market, and a reputation for lenient gatekeeping increases the demand for their services.