There are two types of M1 Carbines: The original USGI issue and the commercial versions. If it is a commercial version, take a BIG step backward and keep walking! The commercial versions are generally not very good (and they tend to cost the same as a GI gun).
In order to find out whether it is USGI or commercial, look at the manufacturer. If it is a USGI gun, you will find the manufacturer on the receiver, just under and behind the rear site. This website lists ALL manufacturers of USGI M1 Carbines, and a short history:
http://fulton-armory.com/M1Carbine.htm
If it is not made by one of these companies, it is to be avoided at all costs. Companies that made commercial verstions are: Iver Johnson, Plainfield, & Universal.
There is a new batch of commercial carbines that have just started to be released. The company is called IMI. I have heard good things about these guns, however, I'd still go for a USGI model...
Is this gun worth $500? Hard to tell without looking at it in person. If it is a commercial version, I would pass on it. You can find USGI carbines at most gunshows for $400 and up.
HTH!
