i've had this happen several times in the past. An honest buyer with some integrity will want to do the right thing and either pay for the item or return it. Perhaps the buyer still wants the item - you can message the buyer and have them pay you through Venmo or Zelle. If the buyer no longer wants the item (maybe they already purchased another after you refunded them), you can tell them to return the item by refusing it. USPS will return an unopened package to the sender if it is refused.
Here's how to refuse a package through USPS:
Write “Refused” on the mailpiece. I’d suggest doing this near the postage area, although that can be hard to find on some pieces of junk mail. I tend to use a black marker for it to make sure it shows up, but I’ve used a normal pen and it works just as well. Or if you do this a lot, you can even have a rubber stamp made up (they’re not very expensive) and use that.
(Optionally) Make a few dark marks through the barcode and address. This isn’t always needed, but it can help make sure that the automated sorting equipment doesn’t just redirect the mailpiece right back to your mailbox without anybody looking at it. You don’t need to obliterate the address or barcode, you just need to do enough that it won’t be read automatically.
Give it back to the US Postal Service. Essentially, put it wherever you put the rest of your outgoing mail. I just put it back in my mailbox and raise the flag. If you prefer, you can stick it in a regular blue collection box, or even go into a Post Office and hand it to a clerk there. The mail just needs to get injected back into the mailstream somehow.
You can only refuse unopened mail. If you open the mail to see what’s inside, you need to throw it out or recycle it yourself, since the Postal Service won’t take it. By opening it, you accepted the mailpiece.
I've used this method to get packages returned to me without having to pay USPS shipping again to get my item back. Only fair in this instance due to their delayed delivery of the package.
