If you're planning on getting the game after it is released, I would strongly advise against using eBay. I got my first copy of Pokemon Diamond off eBay (apparently brand-new and factory-sealed), but after playing for a couple of weeks my pokemon summary screen had a really bad glitch (a portion of it had been invaded by evil random-coloured squares D: ), and it occasinally froze when I entered a battle. Thinking this faulty game was just a one-off, I bought a second copy of the game (again from eBay), but my save data frequently got deleted (I suspect the internal battery had died), so now I just play Platinum (which my mum got me for Christmas, but I don't know where from).
Moral of the post: Don't trust eBay!!!