I have been on both ends of this type dispute. The seller is definitely at fault if the frame is not as advertised.
I think that Paypal/ebay will say that the buyer must pay shipping in exchange for a refund in this type case. It's just a chance you take using ebay.
As a seller, once I had a buyer request a partial refund saying the item was not as described. They liked the item & wanted to keep it but did not want to pay as much as their bid...WTF.. I put it in his court. He pays return shipping & I refund bid amount. Paypal/ebay agreed with me after some deliberation. Buyer kept the item.
Not saying any of this applies here except ebay said the buyer must pay return shipping in exchange for refund.