I shipped out a 1907 IH on march 9th. Recieved it back today saying "return to sender -attempted Not known" and Opened by mistake written on the envelope, Don't know person. Envelope was still ripped and the funny thing is, I got positive feedback soon after I shiped it the first time. Will attempt to contact tomarrow to see what happened.
FWIW, you either have his phone number or can easily get it from eBay. I think I would call before I did anything else.