Have most of you guys forgot the lessening of the guidelines post the introduction of the flag system? Yes, you can now leave negatives for many more things (and no, it isn't abuse/misuse like it was before - to a lesser extent now). It is the flag system that's for scams nowadays, and the trust system for more "opinionated-things".

You should give these ratings for anything which you think would impact someone's willingness to trade with the person, but you should not use trust ratings to attack a person's opinions or otherwise talk about things which would not be relevant to reasonable prospective traders.