Honest Guide is a YouTube channel for people interested in visiting Prague. It's got tips and cautions that are great to know about in advance of going there. I wish there were similar YouTube channels for other places.
In its latest episode, Honest Guide describes five common scams that tourists should watch out for. The most interesting one is not so much a scam, but a sucker bet. Some guy has built a structure with a horizontal bar, sort of like a pull-up bar. He sets it up in the middle of Wenceslas Square and has a sign that tells people that if they can hang from it for two minutes, they make 5 times the money they paid for. But no one can do it because the bar spins, making it impossible to hang from.
The host also recorded a recent encounter with a scammer who drove up to him in a Mercerdes while he was sitting on a sidewalk bench. The scammer explained that he had lost his wallet and needed to buy gas. He gave the host his "valuable" ring as collateral, but the host started recording the scammer. The scammer threatened to call the cops, and when the host encouraged him to do so, the scammer quickly drove away.
(One of the many reasons I like Japan is that in the 8 times I've been there, no one has ever tried to cheat me.)