In order to avoid bounty scams you need to consider 2 things:
1. CHECK THE PROJECT - you need to do research about the bounty, the project team, the whitepaper because some might just copy and paste it, the advisors, roadmap, bounty pool and ofcourse the founder you need to be a good observer, check their background because sometimes by just merely observing and reading you will know right away if the bounty is a scam.
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.
thank you for your kindness!
hope it helps!
more power!
3.
DONT JOIN THEM - Bounties are paid in tokens that is close to have little to no chance of being listed in a good exchange. You might be left holding something that has no value.
Some bounties might have used many fake forum accounts to trick the real accounts that many people want to join the bounty.