If you refund incorrectly, then this can happen.
A buyer needs to open either a returns case or a case for item not as described. If the latter, the you have to pay for that fully tracked return postage and you do not refund until this is shown by the Post Office that is has been used, that is, the item has been posted.
Only then should you refund, through the case details, and within 8 days to avoid a damaging defect on your account.
If you refund any other way, and before you receive your item back , there is then no way then, to enforce that buyer to post back your item.
