You need to accept the return, provide a label and refund the buyer when you get the item back.
Even if you don't accept returns, the buyer is covered by the Ebay Money Back Guarantee and can return the item if they say it is not working properly.
If they send back a different item, then come back for more advice before you refund.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
