I have never had a problem, nor given or recieved negative feedback.
But i do agree with Bert and Sidedraught that the feedback has its flaws to the point of being pointless.
I dont bother giving feedback much anymore.
One seller i purchased from, sent me an email 3 weeks later asking that I leave feedback and they would then do the same for me. I replied to him ' Mate you waited 3 days to receive my money and see my good faith. You had nothing to lose. I sent money and waited a week to receive my goods and see your good faith. I had money to lose. Now tell me why I should give you feedback without you give me feedback first?
No reply.

Feedback is pointless unless the seller is required to give feedback first.