I'm not familiar with that machine... but generally... just check to make sure that it turns freely, that the discs are tight and don't wobble... look for blade cuts on the top of the bar that might indicate that it's had bad bearings or bent blades. Look for leaks. Check for busted shoes. Look for rock damage on the discs. Generally if it's got a lot of rock damage it's going to be a nightmare... Number one thing on your list... BUY it CHEAP then if it does blow you're not out a whole lot and you can either fix it or cut your losses.