They are good rifles, and too often they are under-rated simply because they are so inexpensive. When fed good ammunition they can shoot surprisingly well. The only real complaint I have against them is that the safety is awkward to use, but on the range the rifle can be made safe by simply opening the action so I never use it anyway.
A good ones have stamped, matching numbers on the bolt and receiver, and a crisp trigger pull. It will have a smoothly machined receiver that's dated 1941 or earlier, and an excellent bore and crown.
Avoid the ones with mismatched or electropenciled bolts, creepy triggers, or late-war receivers that were obviously coarsely machined under wartime conditions. These guns can shoot well, but they are a riskier buy.
All the surplus ammo I've seen is corrosive, which is fine if you _always_ clean the same day, and used a water-based cleaner for part of your process. Some of the surplus ammo is quite good, and some of it is awful, inaccurate, jam-inducing stuff that can make even a fine rifle act like a dog.
If you reload, you can pull the surplus bullets, replace the Russian powder with a softer load of new powder, and seat the bullets back again. You can load them down to 30-30 levels if you like and they are very comfortable to shoot.
You won't find a more reliable, more accurate centerfire rifle for $120. Buy the best one you can find and enjoy it.