My buddy was in a bar in Volgograd and somebody tried to sell him weed.. he declined the offer. A few minutes later the police came in and asked to search his bag, he said sure, there was a bad of it sitting right on top of his things in his bag.
Turns out there's a reward for turning drug dealers over to the police. So the guy he met was going to sell him the drugs and then turn him in to profit twice. When he refused to buy, the guy just planted them and turned him in any way.
Buddy spent several years in an Russian prison. The American embassy couldn't help him.