I'm pretty sure DT will negs trust both the seller and buyer and no more sig camp for them 
Just look at how many negative tagged members are participating in bounty campaigns. 
as far as I know, having negative trust would get you kicked out of sig campaign
I'm not talking about negative untrusted feedbacks but trust feedbacks that really count
and I said sig camp not bounty campaigns like you pointed out
aren't those bounty campaigns requiring certain number of followers instead of forum's rank?