If I go into a well known trading card store in my area you think they could tell by looking at it if it is a 9.5 or higher? Not really sure how to tell by looking at cards. All I know is no corners are bent or anything and are in toploaders to keep protected.
Centering is going to be the main thing, and sure someone who runs a card store "should" be able to better tell you what grade to expect. It would really just depend on how familiar they are with graded cards, though. Some cards I see grade out well and I just wonder how the heck they would even grade centering because of the card's design so I really couldn't help you with that one.
The only things you could really check yourself, or at least as far as I'm concerned, are corners, edges, and the surface. The corners should be perfectly sharp. I mean not even a slight rounding. You're looking for four perfect 90 degree angles. Make sure there are absolutely no dents or knicks on the edges. Finally, hold the card so the light glares across the surface and inspect every inch for scratches. If you can't find a single thing wrong with the card, chances are it'll grade out good. Remember, though, the guys at Beckett will find everything you see and, possible, some you don't.
I have 3 graded cards. They all have four 9.5 subgrades and I can tell you that two of those cards look absolutely flawless to me and my eyes. Those two, I'm not sure how/why they didn't get 10s. It's obvious, to me, that Beckett sees things that my eyes can't. Either that or they didn't like the players on the cards.