I had a situation a year ago... a little different but still somewhat the same.
I bought a pair of goalie pads from a guy in the US. He had two pair for sale.
I win, I pay, he ships. The wrong pads arrive. Then a day later the correct pads arrive. Turns out he took them to MBE and they shipped both pair to me in error.
I contact the seller, tell him I have both pair in error. He gives me the rightful owners address in California and asks if I would ship them direct to him and have the charge directed to MBE account (authorized by the agent at MBE).
UPS comes, picks up the pads, then several weeks later, I get a bill from UPS for the shipping of the pads from us in Ontario to California. Turns out you can't ship to a US address and have charges directed to a third party also in the US. Damn......
The vendor gives me some grief, saying it isn't his problem it was MBE's fault they shipped them to the wrong address and I should be attempting to collect from them. I finally convince him that I was just trying to be a good guy by shipping direct to the proper purchaser on his behalf and I should have just sent them back to him and let him sort it out.....
It did take forever, but finally MBE was able to convince UPS that they had made a mistake, and the charge was reversed to them.... but it was nerve wracking at the outset as the bill was in excess of a couple of hundred dollars.....(by the time all of the charges, fees, duties, late charges, etc were added).
Good luck on your issue...
Jeff