look for bubbling/roof rust at the front and rear. take off the bottom of the seal on the body in the tailgate area they are also prone to rusting underneath when water gets trapped.
rear shocks are also prone to be rooted as rvrs squat hard under boost so that can be something to bargain with.
would probably be wise to pop the intake pipe off the turbo and check for play. ideally take a compression tester but thats not always feasable.
beyond that theres not much that is a major issue that is hard/expensive to fix.