If you do your homework, you'll be fine. Decide on a gun or two you're interested in, and watch the youtube videos explaining how it comes apart, which o-rings cause problems, etc. I bought a used DM9. Several bad o-rings and the macroline looked like a dog chewed it--Leaking in several places. I sorted out those issues out quickly because I had done my homework. As others said, seeing a shooting video is a good idea. Also, I used EBay because I was comfortable with their dispute resolution policy (although I've never used it).