I have not owned or seen a c6-n, but here is a link to a review -
http://www.derbyastronomy.org/CelestronC6NReview.htm
The reviewer gives a favourable impression.
I think if the optics are good - dos not matter how old a scope is, we had some really old miroscope(s) but they were beautiful to use if they were maintained. Sometimes old stuff is better than new junk.
The rpice seems ok for a 6" scope on a decent mount.
Get the guy to let you have a look through and show you how to use it first - before you commit to buy.