^^Yup, case damage is sometimes hard to see at first, so look carefully and watch for painted-over JB Weld. Just sayin'...I've seen some really bad fixes on Banshees and I'm sure 'Zillas are just as suceptable.
Take and use a compression gauge, also check the rear axle bearings and swingarm bushings for wear. Same check for frame cracks. Pull the radiator cap. What's in there? Nice clean coolant? Only water? Rusty goo?
How's the air filter? Hopefully there's one in there... Dirty, clean, downright nasty?
Check chain and sprockets...
How many kicks does it take to start when cold? More than 3 and the carb is outta tune or something else is wrong.
Check your trans oil, too. Same idea here; see what kind of shape it is in and go from there..
One more thing I look for on older quads...call me odd but I'm just quirky...Look at all the hardware holding the bike together. Is it all the same, or do you have mis-matched (or even non-Metric! - Gulp!
) fastners all over? Screw heads all stripped-out, or everything in order? This will give you an idea if things were put together well or just thrown together by the owner at the last minute.