On Doctors, Mechanics and Computer Specialists or Where are the Problems with Credence Goods

With credence goods consumers cannot judge the quality they receive compared to the quality they need. The needed quality can only be observed by an expert seller who may exploit the information asymmetry by cheating. In recent years various contributions have analyzed the credence goods problem under a wide variety of assumptions yielding equilibria exhibiting various degrees of inefficiencies and fraud. The variety of results has fostered the impression that the equilibrium behavior of experts and consumers in the credence goods market sensitively depends on the details of the models. More disturbingly, apparently similar models often lead to contradicting results. The present paper shows that the results for the majority of the specific models can be reproduced in a very simple unifying framework. Our model is constructed so that an efficient solution is reached if a small number of critical assumptions is satisfied, and virtually all existing results on inefficiencies in the credence good market are obtained by relaxing one of these conditions. Thus, our simple unifying model not only permits a clearer discrimination between situations in which market institutions solve the fraudulent expert problem without any cost and those where they do not; it also helps to identify the forces driving the various inefficiency results in the literature. Existing results are generalized, some previous interpretations of the forces leading to the striking differences in outcomes are questioned, and a new source for inefficiencies is identified