btackett30...
Just as everybody else here has said make sure you do not use friends and family PP. Take payment via goods and services.
I had a deal just like this last year with a member on another form that ended up giving me headaches. But I was well prepared and I was able to stop the problem before it even started. Here is what I did and always do with somebody I don't know.
I videotape the whole process of wrapping up the knife and packaging it. I show the knife and detail and I show entire packaging process from start to finish. Then when I'm wrapping up the package I put small tags on the seams, corners and edges. I videotape those tags closely and then I cover them up with more clear tape. That way I can prove what the package looked like before it went out. Then when I go to the post office I make sure that I get the weight of the package documented. I also film the package after the postage has been put on it showing those same tags that I put on the box earlier. So if he comes at you at a later date and says that the package was tampered with he has to show pictures that it wasn't packaged properly or it was tampered with. Then the USPS will have to honor the insurance. But with the signature required option he won't be able to say the package was tampered with during delivery because he accepted the package. Then make sure you get signature required and keep your receipt and tracking information. Also make sure you insure the package for the value of the item.