A basic single transit ticket in Berlin is good for two hours of travel - meaning you can get off of the subway, tram, or bus and then get back on later if your time hasn't expired. This, coupled with the fact that most people's tickets expire while they are at their destination, even though their trip may have only taken 15 minutes have led to an underground economy of transit ticket resellers. These resellers, who can be found at virtually every subway station in the city, often work in teams asking people exiting trains for tickets that they are no longer going to use.