There are so many folks out there ready to cheat you I would be very hesitant to do this.
I have bought both my Pfaffs used - one from a dealer and the other from Craigslist. I went in person with cash and had her demo it in every option (embroidery, button hole, decorative, straight etc) before I bought it. Worked beautifully - I was convinced that there was nothing majorly wrong when I walked off with it.