I lived in Chiang Mai and remember the police shakedown checkpoints very well. I was privy to seeing them being not at all secretive about the fact that they were pulling over all tourists and then fleecing them for a bit of money. I always wondered how it was that they could tell the Chinese tourists from the native locals but then I later found out that all motorbike rental shops are obligated to display a large sticker on the front of the bike indicating it is a rental.... and there you have it. The police stand and look into the distance and simply flag down anyone on a rental bike and this equals easy money.

But I agree with most of what you wrote. Getting fussy and filming them is going to make your day a lot worse... they might just take your keys and not give them back. what are you going to do? Call the police?