Allocating appointment slots is presented as a new application for market design. We consider an online booking system that is based on the principle of first come, first served which allows scalpers to enter the market and sell slots to appointment seekers. This is inspired by the booking system to obtain a visa at a German consulate. We propose an alternative system and test it experimentally. The alternative system collects applications for slots for a certain time period and then randomly allocates slots to all applicants. We investigate the two systems under conditions of low and high demand for slots. As predicted, scalpers profitably book and sell slots under the immediate system with high demand, but they do not make pro fits in the deferred system under both demand conditions.