This trick uses an unusual pack of playing cards, each card is shown to the audience to have a different back design. The magician deals through the cards one by one, a spectator calls stop at any moment and a marker card is placed in that position. This is repeated with a second spectator. The cards are spread and the two chosen cards are removed along with their markers. When the chosen cards are turned over, they are seen to match the markers both front & back. Then the remainder of the deck is spread face up, it now shows to be an entire deck of cards of the same face value, totally different to the chosen card values.
A trick with impact that's easy to do.