Patt, I'm not familiar with the Seleco 350 specifically, but 6500+ hours are probably enough to toast the tubes of virtually any CRT projector, if it's been driven hard. If it has displayed a static image all these hours, it would almost certainly have severe burn-in on the tubes.
I would say that it's essential you check the tube condition before parting with your money, preferably by viewing the projector in person, with the lenses off. Be wary of photos too; I know from personal experience that mild wear may not show up in a photo at all, if you just take a simple shot with a flash as illumination.
Here is a link to a page that shows you varying degrees of CRT tube wear and burn-in. May be handy as reference if you're unfamiliar with CRT projectors: http://home.centurytel.net/rshannon/AVS/crtburn.htm