Ask the buyer to open a relevant case (not received or not as described) far right of item on their My eBay Purchase History page. When you accept it if f you don't want the item back you will be able to issue refund without issuing a return postage label.
If the buyer has asked to cancel the transaction go to the cancel link on right of item on your sold page and choose "Buyer asked to cancel", Once buyer accepts it the refund is automatic.
