If they are within 30 days of the item's last estimated date for delivery, they can open a case for item not as described and you will need to fully refund the buyer. If you want the item back first, you pay for the fully tracked return postage and only refund, through the case details, when the item is back with you.
You may have missed the mark when listing / posting, or the buyer may have made the mark, either way it cannot be proved what happened, and the buyer has the right to have it returned, at your cost ( if you want it back) for a full refund.
@lien3383