Specify to the seller that you want to "cold start" it, often unscrupulous sellers will pre-warm vehicles to help hide any starting system glitches, also get a good look underneath of it as bent up & dented undercarriage will also identify a vehicle that has seen a substantial amount of time off-road & any leaking component seals.
Also the automotive mandatory...
- Coolant check for bubbles when idling, and contaminants
- Creamy oil in the rocker cover & on the filler cap
- Colour & odour of transmission fluid
- Transmission shift times 1.2 sec (forward) 1.5 sec (reverse) faster is better
- Electrical system functionality
+1 on getting an independent assessment prior to purchase the Royal Auto Club in your state will offer this service