I'm no expert, but since you asked...
Once the Russians went to war with Germany, their production of these rifles got a little more hurried, and some say the quality dropped somewhat. So, if given the choice, I would look for one from pre-war manufacture (year should be on the barrel) so long as it was in good condition.
Be sure to take a bore light with you and get a good look, just to be sure it isn't heavily pitted or rusted. The main Russian plants that manufactured these rifles were Tula and Izhevsk. It seems that most buyers, if given the choice, lean toward the Tula guns. There is a website... 7.62x54r.net which can help with identification.
Finally, unless it is in impeccable shape, or is a somewhat rare vintage, I would try not to spend toward the high end of what that store is asking. You should be able to do OK for less. Good Luck!
Just the kind of info I was looking for. Thanks.