Note: Buyers can leave sellers negative, neutral or positive Feedback. Sellers can leave buyers positive Feedback or choose not to leave Feedback.

If a buyer doesn't pay for an item, eBay also removes Feedback left by a buyer when the buyer hasn't responded to an unpaid item case and has an unpaid item recorded for that transaction.

http://pages.ebay.com.au/help/feedback/howitworks.html

While sellers can leave a positive Feedback rating and a comment for buyers, they can't leave negative or neutral Feedback.

Negative Feedback discourages buyers from future transactions and can lead to lower sales. In addition, there are more effective ways for sellers to resolve issues with buyers.