Go to the Sheldon Brown site, he has an excellent recap on the various steps to try. About 90% of the time, I have been able to get a stuck post freed up using those steps.
As far as what the seller told you, I am not surprised. I do my own research, as most of what I am told by sellers is wrong.
Looks like a Voyageur to me. I had a 1981 one, that was just about identical.
I would put the work into the seat post first, that can be a deal breaker.
