I have a Gammill PDQ, which is actually a Nolting, but circa 1986. I called Nolting one day with a question and they directed me to a super knowledgeable tech, who treated me as if I'd bought a new machine a week ago. I honestly don't know how they do it, but they are great. But mine is a basic machine, and my question was met with an answer that took me to Zoro Tools for a motor. If this machine has a stitch regulator or anything like that, it would be more complicated to fix. So a 10 year old machine itself will probably last longer than us. A computerized part on it would be it's weakness
I don't even know if my machine has a serial number. If it does, I can't find it. The Craigslist machine might not either.
Nolting's web site has used machines. See if you can find something similar and see what they're asking for it.
If you're leary of this Craigslist deal, then skip it. Another deal will come along eventually.