I would box it back up and let the seller arrange for pickup and shipment back to him (and pay for the shipment, and deal with customs, etc). Meanwhile, flag the payment with paypal or your CC company, whichever applies. He sold to a person in a state in the United States, and in most US States, if you receive something you didn't order, you're under no obligation to accept or pay for it. This has been the case since long before eBay was a twinkle in anyone's eye.
And +1 what @
noglider wrote. I wasn't aware of the higher percentage of bad transactions, but it comes as no surprise. That just piles on top of the fact that ordering from overseas complicates returns/refunds.