JMO, next time you look at a used M14 clone or M1A, ask for the parts card. This should contain a list of all parts and it's source. If a USGI part is listed, it should note the ID stamping (will be the drawing number) and the manufacturer's code (SA, H&R, TRW, WIN, etc.).
Any M14 or M1A owner who knows anything about his/her rifle does this. Also, stay away from any reweld USGI M14 receivers (MKS) as BATF, being the jackbooted thugs they are, are trying to force owners to sign abandonment papers.
Here's a list of parts that are stamped if USGI:
Receiver, Oprod, Trigger housing, Hammer, Safety, Rear sight base, Windage Knob, barrel, and probably some more I can't think of right now. Some parts not being USGI is not bad since the cost to replace with such part can be under $10 or not more than $50. However, some are very expensive such as a USGI oprod. An excellent USGI oprod with good geometry and not reweld or bent will cost about $200. You can buy oprods from the CMP for $50 each but I understand that you have to buy 3 or 4 to get one in great shape.
You may find it interesting to call the seller back and ask him for the listing of USGI parts on it. It will be interesting to find out if he is pushing the FedOrd with the cheap repro parts. If so, then he is trying to screw you without lube.