Many of the "Century Arms" guns are parts guns that were built to meet U.S. compliance standards. What they did was take parts kits and mate them to a U.S built receiver. That way they could get around a lot of the legal issues that prevented them from being improrted during the Brady Bill Assault Weapons Scam that eventually went away due to the sunset clause built into it.
Others are imported guns after the Brady Bill went away that are fully operational guns but have the company of import on them. Most of what you are seeing now are various Romanian,Polish and Yugoslav imports.
All of them are good working guns,but there are many variations in quality. They can go from totally sucks to pretty good.
Make sure that you see it before you make the deal. Some have the front sights stacked on at an angle, others look like they were inletted with a chopping ax and are pretty crude.