I know how you feel, i had the same experience, and more than once. For those bounty projects i don't get my pay, my method was blacklisting the bounty manager, maybe some are not manager fault, but i still don't want to work with them. I don't give up too.
Great, this is one simple strategy that any bounty participant can implement for himself, because marking a manager who doesn't pay is a very good thing too, because once they don't pay, they will do it again in the future.