In order to avoid bounty scams you need to consider 2 things:
2. CAMPAIGN MANAGER - the one that you should always consider, because if the bounty manager is scammer then the bounties itself is a scam, and it is really obvious if the bounty manager has a negative trust then surely he or she is scammer, one thing to consider also is the rank of the bounty manager the higher the rank the higher the legit factor, you can always do research here there are many list of legit and reliable bounty manager and the list of all bounty manager scammers.
The first one that I actually look at when I am finding a good campaign is the campaign manager. The higher the rank is, the more trusted the bounty manager because he will not risk his account by managing a scam project and it is an assumption that he is already knowledgeable when it comes to campaign because he is in the forum for some time already. The next to search is a good project. If the project is already a partner of other ICOs then it would become one of the proofs that it is reputable especially if it has successful Pre-ICO. Constant update of their social media accounts is also a factor.