Minor thinks like bushings are often bad. Pay attention to the diff, there are a lot of reports of a nut backing off and the diff basically exploding. Several people have mentioned hearing a "ticking" noise shortly before everything letting go.
Also check for engine dusting - pull the air filter and check the intake pipe and make sure dirt was not going past the filter. There are two schools of thoughts on air cleaner, seems a bunch of people like the aftermarket for better flow, but the others hate them due to more dirt going by the filter and causing engine issues.
Check of the RZRforum for a TON of info on the machines and possible problems.
Good luck on your purchase