Be warned: I'm sitting here wearing a Mosin Nagant T-shirt. I now own quite a few of these guns, and can hardly pass one up if it looks decent. I have one from 1899 that I would not hesitate to shoot, but choose not to. I have two others with hex receivers, I have an M44, a Finnish M39, and an M91/59. I bought one with a bore that looked like a coal mine, and shot it shiny clean.
Everybody here has offered great comments. You will really enjoy reading the comparison of the AR, AK and Mosin-Nagant HERE
These rifles are a legend. I've bought ammo as cheaply as 18 cents per round, and that was last week when I was offered two 440 round SPAM cans of ammo for $75 each. The mid-WWII dates (1942 & 1943) are very common in the crateloads of M91/30 Mosins coming into the country. Most of these have very clean bores and shoot well. The stocks are easy to refinish if you are so inclined. Check for a smoothly operating bolt. Most are. Some are excessively tight, but the improve with time. Be prepared to do some cleaning, but don't buy one so gummed up with cosmoline that you cannot even pick it up to examine it. Pull back the bolt. Then carefully depress the trigger to release the bolt from the rifle, and look down the bore in the direction of a light source. Most of these have extremely heavy rifling and are some of the most over-built guns ever made. They are like portable tanks. With a 28½ inch barrel, any inaccuracy isn't the gun's fault.