Exchange booths with a rate for nobody
Prague — Old Town Square, Wenceslas Square, Charles BridgeVery commonThe board shows an excellent rate that applies only to transactions over a large amount, or is the "sell" rate rather than the one you get. You hand over euros and receive far fewer koruna than the sign implied.
How to avoid it: Czech law gives you the right to cancel and reverse a currency exchange within three hours, and booths must display the true rate. Ask for the exact amount you will receive in writing before handing anything over.
Sources Czech National Bank — exchange office rules UK FCDO Czechia — safety and security