You remove a blue backed card from your pocket it has a large shark stuck on it. You claim that this is your card shark and he will find their selected card.
The shark instantly vanishes from the blue card, the deck is spread and right in the middle there is one BLUE backed card with a shark on it, this really is their card no switch etc. Now for the killer ending, they slide out the signed card it has a LARGE BITE OUT OF ONE CORNERS!