[1]Why are there so many scam bounties out there and [2]how are we to know which is scam or not
[1] Because there are many newbies that can easily be scammed by these scammers.
[2] Its difficult to know which are the scam and not but here are some of clues. If the project is cloud mining and lending platform thats an obvious scam.
Not only newbies. Scam bounty are on the rise. Even products that seem to have product too don't pay bounty. Like Tokenpay. Bounty was done but they were not paid.
A whole lot of scrutiny before doing any bounty again