I was left (on another I'd) nasty negative feedback when I opened a non payment.
The case was closed and the buyer never paid and he was still able to leave feedback. Some buyers know how to do this and go out of their way to do it. I rang eBay and after they looked into it the neg was removed.
So beware if you have a nasty buyer that loves negs, checkout their feedback left for others on their feedback page and that may tell you to expect it or not. My buyer had 24 negs in a row! left for sellers but eBay still lets him get away with it?.