If you have ever been victim of a brown boy trying to extort money out of you for having a scratch on your mudguard or wearing a baseball cap whilst driving or not having your passport on you, I have learned over the years some ways to beat the buggers.
1: If you can speak French, try doing just that so there is no way they can communicate back. If you can not speak French, pretend you can and tell them you are from Moldova, pester them and insist on drawing a map. Don't give them anything and make them wish they had never picked on you, make a big meal of it.
2: Get duplicate copies of your driving licence and hand this over to the bastard who wants 300 baht for it's return.
3: When a policeman who doesn't understand English asks for 500 baht, wai him and say thankyou very much but "Mai ow crap" in the most broken amatuer Thai you can muster. Continue to indicate that you couldn't possibly take his money until he gives up and fucks off.
I can't think of anything else, though if I am not in the mood for giving to beggars I find that walking past them whilst rolling your eyes and mumbling gibberish to yourself subsides some of the guilt.