it wasn't labeled as slow or inop. and so I would expect it to work just fine. I don't think that is naive thinking. I've bought maybe a dozen 50+ year old cameras from keh.com and most of them have worked fine.
Well, I understand that things like this happen and so I am not upset at keh.com. I've never had a contax camera so I was just checking if I was doing something stupid. With the Retina IIIc cameras you have to reset the film advance to fire the shutter...maybe this camera had some weird quirk. I have no idea but that is why I asked. I will fire it a few times to see if it will be consistent.
I'd probably just return the camera or look into servicing it. I sent my TLRs for CLAs in the past but I have no idea who services Contax cameras outside Henry Scherer. I mostly use Leica M but I had the urge to try the Contax, for fun.