When I was first starting out (waaaay back about a year and a half ago) I bought a Calumet 4x5 on ebay. I would have liked to build my own, but I don't think I had ever even seen a large format camera in person, so it was a little hard to picture how it worked. The camera was advertised as being in working order.

I got it, took it out of the box, looked it over for a couple of hours, spotted that the rear end was broken (and thankfully it was visible in the pictures on ebay so they knew it wasn't me). I sent it back. But what I gained from just looking it over was invaluable in understanding how it works, so then I was able to build my own.