A good running shoe store:
1. Will not be afraid to strongly discourage you from a shoe that simply catches your eye, or your "new thing" radar.
2. Will have severe misgivings about letting you buy ANY shoe without running at least 200 meters in it.
3. Will counsel you that most often, the most expensive shoe is NOT the best for you. (Sometimes, maybe every 5 years or so, it may be.) And they'll bring you out one to compare anyway, so that you can feel for yourself which shoe is, in fact, "you".
4. Will NEVER suggest (or let you suggest) a larger size when you really need a wider one -- and they will explain WHY, and tell you where to find what you need if they don't have and/or can't get it.
5. Won't try to push high-margin insoles that you don't need on you.
6. Won't eyeball you walking or running across the store and tell you that you overpronate and thus need support/motion control.
7. Won't use your static arch height to assign you a shoe from the neutral/stability/motion control categories.
8. Will have staff that can have a good conversation with you about your training habits, what you do/don't like about your current shoes (if not a new runner), and what your past injury history is.
9. Will have staff that are shoe geeks who have personally run in a lot of the shoes that they sell (recognizing of course that new staff may be less experienced initially, but should be supported by those more knowledgeable).