If you have a message from the buyer asking you to cancel the transaction you may be able to get the defect removed. Give eBay a call and try. Apparently the eBay CS reps are now able to remove defects if the buyer has contacted you prior to issuing the cancellation request and you used the reason 'buyer changed mind'.

http://pages.ebay.com.au/help/policies/defect-removal.html

On ebay.com buyers will soon be able to initiate cancellations which should reduce the number of unwarranted cancellation defects.