With negative trust if no one can participate there are many participator who joining many campaign...
is it risky for the participators
?
It's not true. There are so many bounties who accept even red tagged users. I don't know why, because such promoters can damage project reputation. Maybe some managers just don't care about it or it's scammy project.
If you're not doing wrong things on Bitcointalk, you shouldn't be worried about negative trust...