Reading, searching and intuition are my implementations for myself in joining bounties. It's hard to join in many bounties just select which projects you may think have future, demand and progress. If I have atleast 10% doubt about the project, I won't join.
Thats what we should do when joining in bounties.
Conduct a research and only choose the project that is likely genuine and dont rush joining if you're not really sure.
This can prevent ourselves from participating in not worthy project to advertise.