Based on my experience with my Century R1A1 FAL, I'd go through the Fal Files with a fine toother comb and learn what to look for BEFORE buying one.
My R1A1 runs now, but I had to send it back to Century. When I got it, the hole in the receiver though which the gas piston passes was drilled off center. This cuased the piston to bind instead of dropping through freely. To their credit, without giving me any grief about it, Century accepted the rifle back for servicing and reamed out the hole so that the gun now functions fine. I only have about 50 or 75 rounds of SA Ball through it, but it had zero malfs. One of these days I'm going to put a low-powered scope on it.
IMO $650 is at least $100 too much for a Century FAL.