Can you post a picture of the magazine door open and showing the inside of the magazine. Frequently, there will be a diagonal line on the inside bottom of the magazine that shows it was dipped and reblued. Not always there but this is something I look for and have seen on many reblued receivers. (This finding is thanks to Joe Farmer who first pointed it out to me.)

If the bore is in good shape, the receiver probably is not reblued and the carbine just has been little used and well cared for.  Great find. As Dick pointed out, if you find an M1896 carbine rear sight and paid full price for it, you would still have a great find at a great price!

Congrats and good luck at the gun show!