Refund the amount for item only. He has no right to a refund of the postage. You aren’t under any obligation to accept return, so can refuse, but as he has sent it, you’d then have to post it back to him & I’m sure it would be “lost” & not reach him. 48 hours is b*ll*cks, as ebay state within 6 days to process a refund. Stand your ground!
Ensure ALL communication is within ebay, be polite, but firm & demonstrate you are being reasonable (you have a no returns policy, the item is as described, but buyer has decided to return anyway), so just refunding item amount, excluding postage, is perfectly reasonable. Ensure you also remind the buyer you’re a private seller, not a business seller, so have no obligation to accept return.