Um, factory sealing obviously means it was never used.
To me, if it is opened, it isn't new. I have no idea where it has been just like a used game.
I have bought a couple of "new" opened games from eBay, all of which looked used. There was absolutely no way they were new.
GS is also guilty of this, and it has happened to me.
About a year ago, I decided to go for Killer7 for the GC at a local GS. They only had an opened "new" copy, but it was only $10, so I grabbed it because it wasn't full price.
To my surprise, I got home and found adhesive on both game discs. I normally look before I buy used stuff, but I took the benefit of the doubt with this "new" game and didn't check it.
The store did let me exchange it for a used copy which happened to be pristine of all things.
Anyway, I've learned a lesson: don't go for anything "new" opened at GS, be it a 50% discounted game or not.