...This is why I don't handle used games often...
Oh, gosh...it slightly sounds awesome, but is more attributable to a nightmare. Just setting foot beyond Nuvema Town into newfound areas with starter Pokemon in tow, and then suddenly WILD BIG MENACING PURPLE METALLIC BUG WITH BACK-MOUNTED CANNON @ LEVEL 100 APPEARED!
Hurry, get away!
I will just post to say that there is always the off-chance that a game bought from a large store could be fake - happened to a friend of mine with Sapphire ages back from Kmart (although I'd think it's less likely nowadays) in which his game had things like a 'Professor Odd' in it... yeah. That said - pictures tend to make your claim more believable. =p If you did buy that from a store and it's a legit game (came in the official B/W box and all) and did not use any cheating/hacking device, return it.
Yeah...I would say that's there's the
possibility of encountering weird stuff if someone glitched out their game and returned it to a store as a used copy. But I would still say such an occurrence it's rare, and rarer still concerning renowned gaming stores. And I highly doubt that BW would already be sold back used
this early in their life cycle(s). :\
I would say first and foremost to
return the game if this experience is legitimate. This is quite an irrational case, and as bobandbill said, pictures support legitimacy. Otherwise, you
could keep it to experiment with the game to discover unforeseen effects for kicks, I guess...
But if the OP
is a troll, please go away. *looks for RuneScape ignore button; doesn't find it...*