There are already team members and bounty managers red tagged, for promoting a scam, or for not paying the participants after the bounty's end, and for similar frauds. But, in my opinion, and to avoid this headache, you have to take your time studying carefully the project, before spending your valuable time in advertising it. This study will help you to avoid the shady projects that will turn into scams sooner or later.
Studying and analyzing are things that must be done before joining and promoting a project, that is true. But not many people can do it.
I think many people are still having trouble comparing which projects are good and which are legitimate with those that are not. That's why many people are stuck with fraud projects. Is there a best way to do it ?