These types of posts are frequent, I think I'm gonna start a post on pulling together all the points to consider and then post the list as a reference document. Many, including me, would benefit from such a list.
Here goes my couple of first points.
1) Look for leaks, any fluid leaking anywhere, including drips on the ground.
2) If possible, check compression, gauges are cheap (harbor freight) or can be borrowed, local dealer can tell you what compression should be.
3) Test drive train, I push against something immovable while in 4 wheel drive and make sure the wheels spin.
4) Let her run for a while and see if she gets hot, shoot with a heat gun if you have one, again, local dealer should be able to tell you what temp she should run at.
5) Check all grease points for grease and slop, see if pins or bushings show any wear.
6) Put in gear and see if brakes work and hold hard. Test both sides on split brakes.
7) Check all guages
8) Volt meter on battery while running, see if you are getting more than 13 volts or so, to see if alternator is charging.
9) Check oil for water, hydro and engine.
10) Ask if 50 hour service was completed, if so try to validate, that's a critical service.
11) Ask a local dealer to run vin and see if there are any issues with the machine.
12) Did I mention make friends with local dealer?
13) Ask if there have been an issues with the machine.
14) Check all lights and switches and kill switches.
15) Make sure you start when cold, again, heat gun is helpful in ensuring the machine has not been warmed up prior to your arrival.
Post any and all questions on this forum, these guys know about as much as anyone regarding these machines.
Good luck,
Joel