I never actually thought about there being paid agents here, but I guess it's very possible, but is bitcoin something they'd want to be spreading fud about at the moment? Maybe in the future it will become a problem to them.
The first HUGE wave of negative trolls came in June 2011, so when you see "Hero Member" there is no guarantee they are here for positive reasons.
Surely they didn't stick around and make a post every fortnight to become a Hero member. It's rare that you see a Troll Hero member as well.
That would be the best tactic actually. To first gain credibility and then start to influence people with FUD.