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 ?
Can you please specify. Do you class an ICO, that do not succeed for an X reason as a scam as well? To my knowledge scam means fraud or dishonest deal.
Simplest decision for you, if you afraid of scam, will be to connect to bounty campaigns when project already raised softcap. Yes you will get not a full income, but you will more sure in choosen project and will get your tokens faster.