If the Bounty Manager knew that the project is scam and still promoted it than they deserve a negative trust.
But if they didn't knew about that, they are no different from bounty participants as they get paid to advertise.
If bounty manager are to be given negative trust for working on a scam project, bounty participants too deserve one as they too promote for payment.
Seems logical. Red trusting a bounty manager without any proof that he pushed through the campaign knowing that it's a scam is illogical (once). But if the campaigns he always promote turns out to be a scam, i think it's logical.
Besides, joining a campaign is decided by the bounty hunter himself. If it turns out to be a scam, too bad, he didn't researched about the project thoroughly.