That's the badside of some bounties,the team behind the project do not pay after the success,they become greedy . Well, when im choosing bounty to participate in,i always consider the BM who manage the campaign,then im checking website,whitepaper and telegram group and allocation ofcourse.And im using also my own self instinct,it really helps.
Gut feeling i would say will help you but you also need to ask suggestions from old members of this forum. Yeah, number one consideration should be the bounty manager because he is the one in charge and he will be the first person to know if his bounty campaign is scam or not.