I disagree on this. Feedbacks and reputation are not things that work out in isolation. Many users give negative feedback or positive (but mostly negative) based on the proof presented by others and that's how it should work.
I agree with this, but this is different from what I was talking about. It's ok to rightly tag someone with red paint if that someone is a proven scammer as a warning to other members.
I was talking about actual cases where two users traded physical/digital goods. If I was part of such a trade with you, and I was satisfied, I would let those feelings be known using the feedback system, regardless what your other ratings say. It works the other way as well. You could have 50 positive trades, I am still going to leave you a negative if you scam me and don't fulfill your part of our agreement without thinking what the community will think of me.