For the most part the engines and frames are solid. It's the small things attached to the frame and engine that typically cause problems. If you have the tools and basic skills you will be fine. If you have or can tap someone with a great understanding you are that much better off. But for the most part every piece on a china bike is designed to be fixed on a side of the road with hand tools and a basic understanding of how it works.
A decent seller is half the battle. Both Killer and APSC are fine. I would call and talk to both. At the very least you will have some answers and a feel for who you are dealing with you may even be able to work out a better deal.
You may be able to get a good deal on this. I know he has had them for at least 2 years but he has always had them priced at $749 as far as I know.
http://www.apscusa.com/Digger-125-Dirt-Bike_p_88.html
Here is some leverage / cheaper models you have to factor in shipping for these I think they always charge $180 for the 125's.
http://www.superiorpowersports.com/1...bikes_s/79.htm