Yes, you guarantee the cards are shuffled, but you also add a question as to whether you've shuffled the deck in your favor. A competitor might make the point that they play unopened decks while you manipulate the decks before the game.
That competitor is free to try and capitalize on the expected value of the three gamblers that switch because of it while managing the liability induced by the expected value of the black swan event. In practice, I don't know why a gambler would trust unshuffled decks over shuffled ones. In the end, anybody gambling is a sucker anyway.
