It depends on how much he paid. It's generally not easy to get a full refund, but easy to get a partial+keep the product.
Usually with a full, you have to pay to ship it back (insured with signature, costs more than what you originally paid). Once they get it, they determine if it's in the exact condition they sent it, and it's up to them if they want to accept or deny the refund claim at this point.
With partial, you simply send pictures showing how it is not what they claimed and discuss what you feel is the appropriate refund.
I've been in the eBay buying and selling business for about 11 years now. I've never had anything returned or refunded that I've sold, however I've done plenty of returns/refunds from buying.
Sometimes the seller will send a replacement at their expense (in one case, an entire mattress) other cases, a 50% refund.