Are you specifically being targeted with ads for stuff? Just a little confused by the first sentence from your post.Abuse of the system or cool?
Cool IMO. I've been using it to flag people doing stupid stuff in the newbie section, like "Hello post" spammers or people who necro old threads. It seems to work as a good way to get someone's attention to stop them from doing thigns like that.
EDIT:
Choo Choo Motherfuckers!
Well depends, if you think they are spamming to gain a good account then scam then flag em till they prove themselves I guess.
They want me to do things like go to their casino or invest in some random alt coin.
Shit like that.
I would definitely flag them using the trust system then if they're trying to buy rep for sketchy looking stuff.