If the seller had just bought it and turned around to sell it, I'd say 2/3 of new. This thing is 20 yrs old, so I'd start at 1/2 of new. If you're really interested, send him an offer and walk away. If he doesn't get any bites at that high price, he might call back.
[Edit] I read it again and looked at the picture. First, that picture seems too composed, like it's lifted from some other source. Also, the text says that it's "been in storage for several years", which is a strange thing to say about something that's unused. I wonder if *he* never used it, but maybe the former owner used it? Hard to say but fishy.