Yeah, it's a very complicated system in place here (IMO).  There's the DT list, there's your own personal trust list, there's the flag system--I'm not sure how a typical newbie makes any sense of it.

The bottom line is that if you're looking to do trades on the forum, you should always check a member's feedback history and check what's written there carefully.  Sometimes a member will have a net red (negative) trust score but might not necessarily be untrustworthy when it comes to trades.  As it stands, any member can leave feedback for any other member for any reason, and the feedback might not always be accurate. 

Good luck trying to make heads or tails of it, OP.  Given enough time on the forum, you might be able to get a sense of how it's supposed to work but it's up for debate as to whether it's the best possible system or some god-awful Rube Goldberg contraption dreamed up by a math nerd.