A test drive will tell a lot......any major problems should show up. Take a buddy with you to watch the exhaust and see if it smokes any when you crank it up or throttle it.
. shift the transfer case thru all the ranges and make sure nothing makes any funny noises while driving...
Ck under it for unibody damage from any previous wreck..... ck around the steering box mount area to make sure not cracked.....
if its been wheeled crawl around up under it good and look for any damage.
Reach behind the dust cover and feel the front rotors if they cant be seen to tell if they are grooved.
Ck the fluids........ clean ? Low ? burnt smelling ?
If the test drive does ok and nothing is bashed up id hold out 6 $100 bills and ask will ya take $600 for it