Summary This study examines the limits of global corruption indicators based on experts' perceptions. It draws on a wave of original surveys conducted in eight African countries that combined two types of approaches. The first approach covers a sample of over 35,000 people and uses experience-based questions to measure petty bureaucratic corruption. The second (Mirror Survey) reports 350 experts' opinions. A comparison of these two sources paints a clear picture of the experts' errors of assessment. We also find evidence for ideological biases, with experts tending to rank countries based on their own political preferences, and the existence of an erroneous implicit cultural model of "how Africa works".