My first concern with used MTBs is always the suspension.
If I were you I would research the cost of rebuilding the Headshock and the rear shock. I would also look at replacement costs for modern versions ... might be worth it if the shocks are done.
I bought a 2007 Cannondale Rize 4 and love it---Love it. The first thing I did was research rebuilding the shock and fork, because on a used MTB, that's where the money will go. Everything else costs whatever parts cost--reasonable if you buy off EBay or buy a donor bike or whatever. But the shocks and fork---can't ride without them and maybe can't fix them yourself.
Do the research, understand what you are risking, and make an informed decision. I did and I am very glad.
The fact that the guy at the shop seems honest is a big plus.