Once your buyer opens an Item not as described case they are guaranteed a refund whether or not you agree. Ebay never sees what is sent so they nearly always agree with the buyer in these cases,.
If you refused to send a return postage label your buyer can ask ebay to step in, and they will usually refund and tell them to keep the item as you don't want it back. Plus you will have got an account defect.
You can only ask your buyer to return the shoes now, and hope they will do, you would have to send them a label or the postage money to buy one. But they don't have to comply.
