Do you sell regularly on EvilBay? If so you may just want to bite the bullet and agree to disagree on the cause. Your good rating may be worth more to you than the satisfaction of feeling you were right. The old saying "The customer is always right" is in play here. Refund his money upon return (at his expense) but let him know you are doing it under protest. Are you right, probably. Is he wrong, probably. Is it worth fighting over, maybe not.
