This might be an old issue , however i have noticed recently with some non paying buyers that you cant give them negative feedback. You can give positive feedback with a negative comment but not negative or nuetral options. The thing with this is that they gain more points towards stars etc. So in reality you could buy 50 items , not pay and if all the angry sellers leave feedback that person could get themselves a blue star. I think this is something that needs to be fixed. Apart from the annoyance of non paying buyers , its the nuisance of having to get back final value fee's etc.

You can give positive feedback with a negative comment

No.....you can't....... because that's again eBay rules.X-(

Leave a positive rating with a negative comment, and I hope you get reported and a violation against your account.