I'm buying a used 5,1 Mac Pro from this guy on a local auctions site. I've looked at the machine and it appears to be fine. I'm only suspecting he might be hiding something because it's a very low price for the local market. It's even possible the warranty is still valid, because he bought less than a year ago. What should I test for? Any specific programs I should run? Also, what can I check for that would void the warranty?