First - see if they have maintenance records and verify that oil changes have been done regularly.
Next - try to hear it start from cold, you're listening for a rattle from the front of the engine, if it rattles for more than 1~2 seconds walk away.
The two items above are related - if regular maintenance has not been performed the timing chains can fail prematurely, and that's a fairly expensive repair.
The other potential problem areas are a rusty front suspension cross member so inspect that, and make sure the 4WD on the dash cluster turns on when 4WD is selected (don't drive it in 4WD on the road, just let it idle in neutral and select 4H)
Beyond those few you just need to check for the usual stuff on any used car - rust in the wheel arches, etc., oil leaks, these are pretty robust little vehicles, and not noted for being problematic.