Look for a good service history as the main thing. If there is no record of it, run!
Most mechanics will recommend to do oil changes at 5000km intervals, Nissan say that 10,000km intervals is acceptable, so your call on what you look for.
I would also look to see what sort of kms it has done. 60,oookms on the highway would be far easier on it than half of those kms going up bush tracks or on the beach. You should be able to get under and check out what sort of condition the underneath is. Also if its been on the beach see if it has got any sort of rust protection.
Good luck!