The trust system works by referral. Positive or negative trust that you give someone will appear to you and to any members that have given you positive trust. For example, if I give you positive trust, then I will see all the positive or negative trust that you give to other members.
That's incorrect. Giving someone a positive feedback/trust, isn't equal to adding them to your "trust list" (you won't see any of their ratings by default, unless they're DT1/2 members).
To OP:First three responses, have valid points.
Also to make it clear, you should follow these (shown at "Trust" page):
Positive - You trust this person or had a successful trade.
Neutral - Comments. Your rating will not affect this person's trust score.
Negative - You were scammed or you strongly believe that this person is a scammer.