I went back to the antique store where I first saw the M1 Garand for $1250. It came with the CMP case and was labeled SA. He'd take $1000 for it. In his little section of the store, he now has two M1 Garands - same price, same SA label, basically the same condition. I'm still planning on buying from the CMP but I just wanted to see what an SA grade looked like (now that I have more info from this thread). Maybe he's buying from the CMP for $750 (or whatever) and selling them in the store for $1250. No way to tell. He's not an FFL.
If the SA Garands from the CMP are in that similar condition, I'll definitely buy from them.
Maybe not - they're sold out.