The truck sounds like it's in nice shape, it's possible the scratches would be able to be buffed out with a little effort depending on how bad they really are.
In retrospect, I paid $23,000 for my 04 suv with 57k miles, in similar condition from how it sounds but with more accessories, chrome everything, 2nd set of wheels and tires, high end security, ect. I've seen a few 05's go for $27ish in my area but they all had 2-3 times the miles your looking at. More recently there was a 06' suv on another hummer site, with maybe 50k'ish miles, go for $23k as well. Personally I would low ball em an offer in $27-27500 and see where he goes from there.
I dont think you'll regret the purchase, my truck was the most money I've ever spent at a single point in my life and I never had a second of buyers remorse, and I get buyers remorse when I buy bags of shrimp at the grocery store! I've had a perma grin for the past 2 months, my H2 is possibly the best vechical I've ever driven.
