One way to look for rebuilds or if it's been torn down before by what kind of peening/staking marks are around the rear sight dovetail in the rear of the receiver, but it's hard to tell with the earlier (better) adjustable sight because it covers them up pretty well.

You can adjust the sight windage all the way to the left and to the right to look down onto the receiver and the edges of the dovetail gap for them, see if there's multiple stake marks to lock the sight into the dovetail, or if they're buggered. And if there's ones that don't correspond to the sight's dovetail in the receiver's.

Here's a thread that shows an example of what I'm talking about. Scroll down in the archived thread and you'll see the picture.

https://www.ar15.com/archive/topic.html?b=6&f=6&t=258801

if the carbine's marriage to the rear sight is original, you'll NOT see triangular notched stake marks from a chisel that went just outside the edge of the simpler L flip-sight AND the circular punch marks for staking, if it's been rebuilt once or more at an arsenal, you'll see circular punch made divots for the staking like in the photo in the thread I've posted above. If it's a later post-war that's never been rebuilt, you'd see ONLY the circular punch stakes. I'm not sure if later post-war ones ever came with the adjustable better sight. If they had extras to put on new ones made post-'45 or what.

Although I might be wrong on some of the details. The combinations of which receivers with which parts, and how many times and places they're staked is a pretty convoluted flowchart. |

Hard to say a certain value because there's tons of stamps and marks on the parts, the receiver, the bolt, the slide, the barrel, the trigger guard/magwell, stock cartouches, and only certain combinations are going to denote it's all original, then there's things like muzzle and throat wear to determine how "used" it is. You'd have to get pictures of everything and then have a M1 Carbine expert put it all together or do lots of internet searching and book reading on the subject.

Assuming the lowest common denominator, a post-war mixmaster that was re-built and rearsenaled with no major condition problems other than some finish wear and handling marks, I'd say ballpark $1200, but to an M1 collector, certain combinations of parts and stamps and condition can send it from anywhere from $800 to over $2000.