Unlike the usual reward certificate bonuses, bestbuy.com is mailing physical gift cards for preorders of Agents of Mayhem. Shipping is required; you can use in-store pickup on the game, but the GC requires a mailing address.
I was surprised that the gift card was mailed off immediately, even though Agents of Mayhem doesn't come out for another month and change. (I pre-ordered on Sunday and had a tracking number for the GC on Monday.) The great thing here is that the GC doesn't expire, and there's not a brief delay like there is for reward certificates to be added to your account.
Be nice! Don't exploit.