OK, there were 2 arsenals in the USSR that made these rifles/carbines. One is the Tula arsenal and its mark is easily identified by the "arrow in a star" mark on the receiver. The other is the Izhevsk arsenal and its is just as easily identified by an "arrow in a triangle".
Some think that Tula's are more collectible. It's more a personal choice, though, because there is really no difference in quality. I have 2 Tula M91/30's, 2 Izhevsk M91/30's, 1 Tula M44, and 3 Izhesvk M44's.
The other thing to look for is the difference in the stock. Most Mosins are in a hardwood stock. However there is a good quantity of Mosins, long and short, in laminated stocks. Some collectors find the laminate stocks to be more desirable, again a personal choice. One thing about the laminated stock....it is MUCH prettier than the hardwood. I have only one laminated stock in my collection.
Matching #'s between the bolt and receiver are something to look for, but not necessary.
If you're going to buy one around $150, make sure it comes with all the accessories (sling, ammo pouch, cleaning rod, rod guide, firing pin tool, oiler, etc.) If these little things don't matter, try to haggle on price and you may get a rifle/carbine for as little as $75.
If you have any more questions, I'll be glad to help. Mosins are the focus of my C&R collection and I know more about them than I do about any other series of gun produced. Not trying to say I'm an expert...just willing to help
