Used bikes are like used cars, in that if you can't assess them yourself, the best bet is to take them to a qualified mechanic. In the case of a bike, a bike shop mechanic should be able to give it a quick check without hitting your pocketbook too hard (I'd guess $25 or a dozen doughnuts). In the middle of the summer, Tuesday and Wednesday are the best time, since it's peak season and they get a lot of business getting ready or getting over the weekend.
I've got a Fuji Touring, and it's a good bike, but they're offering it for only 30-50% off list (depending on age). That T800 sounds sweet.