BEWARE: You have to buy tickets to use buses and stamp them within a minute of entering the bus. The scam works like this.
Tourists come to the bus. One of them stamps the ticket, the driver gives a signal to the controller on a bus and he blocks the stamping machine. One minute later, the controllers surround tourists and try to intimidate them into paying a ridiculously high fine.
What to do: Do not give in. This is a scam. Insist on talking to the police or embassy. Have fun, you can even offer for controllers to pay you so you will keep quite.
There were four of us. We came to the bus. One of us stamped the ticket. Three others we could not validate because the machine did not work. The local people tried to help us—useless. We go to the next machine on a bus and suddenly two controllers (bus traffic officers) surround us and start screaming that we did not validate the tickets and have to pay a €35 penalty each. At first we start explaining the situations, the locals started to defend us, at no use. The controllers do not take their words and insist on us paying the penalty. We insist on talking to the police and American Embassy. The controllers threaten us with increased penalty, finally they negotiate. They try to make us pay double the fine, then the single. We do not give in. The controllers finally let us go. We complained to local police, but they are aware of the scam and do nothing about it—probably they get their share as well.