How many selector positions did it have? One or two notches? If two, did it have chinese symbols by each one? That looked like this...
If so, it's considered a machine gun, and either dont buy it, or do this....
Reason being, the chinese were in a hurry to import these right before the ban, so they took select fire Type-56 AKM's and put a rivet through the hole for the auto-sear, and had slotted rails. Basically turning it into a Mak90, but the BATF ruled that since its got the hole there, its 'readily' convertable and considered a machine gun. While this was caught onto, some of these rifles had already been sold and not recovered and still in circulation.
Chances are it's not one of these rifles, as some did come in with just the UF receiver but no auto modifications. Just make sure, and now you know what to look for before picking it up. And if it is one of these rifles you come to find out, the FFL wont be able to give you a hard time on a full refund, as he's got a unregistered MG i'm sure the ATF would love to find out about.