) will require YOU to be the mechanic most of the time. If you're cool with that then just go thru the paces of purchase.
Things to look for that I'll recomend; Make sure the RC valves are woking, not just loose but that the servo is actually opening AND closing them. You can find way too much info on how to check this on the site. Does it run on premix or with a functional oil pump? Depending on your pref. and intended use, you can make a choice on this (track use - premix, regular road use - autolube). Check all the normal stuff like tread wear, chain and sprockets. Look for pitting on the forks since it could lead to having it all re-chromed and rebuilt (messy messy).