I am no expert here either.  We use our Rhino around the farm here alot.  The wife hauls rocks with it, I use it for fencing quite a bit too.  Its great to throw all your tools/gear into it and go out and do the job.  We also took it on a fishing trip deep into the mountain.  4 hours by truck, then 7 hours by Rhino/Quads.  I was the only one with a UTV, all the other guys had Quads.  The trail is quite rough, lots of rocks & ruts.  We were out front most of the time.   8)   You won't regret it.  I had a Kawi 700 4X4 with 28" tires, chipped, etc.  I sold it a couple of months after getting the Rhino. 

But back to buying used.  I would give it the usual checkover.  Make sure the tie-rod ends are tight, U-joints are tight, grab the driveshafts coming out of the engine case and try to move them around.  I have heard of a few guys where the bearing went inside the case, and the shaft was then sloppy.  (high milage units)  Check oil level, what color is it?  Check the undercarriage, is it all banged, dented?  That should tell you how it was driven.  Also check the CV joint boots. (8 of them)

I'm sure others may have something better to offer. BUt that is a good starting point.

Not as fancy as some of you guys, but thought I would throw them up.