I'm with the others:
Stick to the USGI Carbines and you'll be good to go, go to the after market commerical Carbines and you're buying problems.
Gun Show Carbines are iffy.
We know the CMP is out most carbines but they still have them show up at auctions, (there are 9 showing now). Some pricy, some not to bad.
If I was going to get one, I'd bite the bullet and get one from the CMP Auctions. You know they will work, if something weird happens, the CMP will make good.
If you're not looking for a collector, you can get a good servicable Carbine at the CMP auctions probably for less then you'll spend at a gun show now days.