So how much has it been used in the last year? He hasn't been specific on repairs. Belts and hoses are relatively cheap and easy that should be expected when a vehicle is (ab)used like this. Why did he buy this, keep it a year, and is now trying to sell it on ebay? Something major that he is not divulging or did it nickel and dime him to death with repairs? Where did it come from before he got it? It sat a lot, humid areas are hard on exhaust and chassis, sun is hard on the clearcoat.
Tires I would bet are original with this mileage and age. I paid $1650 for 8 Goodyear G670RV earlier this year, a pretty good chunk of change to consider as part of the purchase price. If the trans is a 4L80E it is marginal for a vehicle this size. I would worry about it more than the engine, especially if you have a toad.
Baggage door, why wasn't it replaced? Maybe it was more than his skill level, maybe more damage than just the door. I don't understand people that buy parts but don't repair the item before selling, it would be better IMHO. He mentions that the skin needs some attention, but no pictures. All in all there are very few pictures for a purchase this large, none of the damaged area, no closeups of anything.
The service contract will probably have a transfer fee, what does it cover and at where do you go for repairs? I am not a fan of service contracts, too many horror stories especially with an older vehicle and not knowing details of the contract.
Have you talked to the owner? He is somewhat reluctant to divulge details from reading the Q&A. I always assume people try to sell something this large locally before paying the ebay fees. If it hasn't met the expectations of buyers that can inspect it I tend to think it is on the low side of average, better to not be disappointed than spend big $$. And 0 feedback so no real history to judge him.