I can say 100% that 60% of all bounty is a Scam. The reward for them is either given and the tokens will lie on your wallet forever or do not give at all. Then what's the point of doing this ?
It is hard to estimate the scam amount in bounties, but on the other hand I find it rather easy to estimate bounty tokens which gets dumped extremely hard because teams are just ignorant and dont care, the amount is 80%.
I even was involved in absolutely awful project CAPITAL TECH where bounty tokens were paid out before the end of ICO and not locked, price was trashed by 95%