If its a good deal it will be sold in a few minutes. First see if its a scam. About 99% of the really good sounding deals are scams.
I evaluate the seller as much as I do the camera. A seller who can't tell you about the camera or avoids direct answers is hiding something. Its a fact that some cameras have intermittent issues and you can't find them in a few minutes, all you can do is to see if it had good care, no bad dings, and that the seller takes care of his things.
You cannot check the shutter count without a computer and software, so its not something easy to do when looking at a used camera. Ask about it, of course.
Good luck, after all I've said, I've never had a issue with a used camera that I bought, and I've bought dozens.