Ask if the seller has the maintenance records. If they can't provide them I'd stay clear unless you like playing catch-up. The things I'd check:
- Front and Rear diff. fluid changed.
- T-case/tranny fluid change.
- Timing belt/chain changed
- Don't forget to take a really good look under the vehicle.
- Check oil pan and all skid plates for damage.
- Check for any hanging oil drops (at all engine to tranny to tcase locales) and Ring and Pinion seal where drive shafts mount to diff'ys.
- !!!Try and use all 4wd positions and switch them in and out to check for inconsistency.
- When looking at the vehicle, make sure the engine is cold. Have the seller start the engine while you stare at the exhaust tail pipe. Make note of smoke, if any at all comes out.
*** If you already know the routine cool, I just hate to hear the sorry stories from people that didn't have the sense to check ALL the obvious wear and tear points. Believe me I've over looked some too.
Paul