A certain card manufacturer had a defect in which there were tiny deviations in the designs on the backs of their cards.
What they would do was the dealer would show all cards face down and Ivey and his accomplice would have the dealer rotate the cards so that the designs were all the same way. Then as they would play, they would have the dealer rotate the numbers 6, 7, 8, and 9 (which are the good cards in Baccarat).
This way they could spot all of the good cards face down based on the designs on the back. Ivey made sure to request a card deck shuffler to ensure the cards weren't rotated during shuffles.
Ivey won tens of millions of dollars doing this and is now being sued by several casinos even though he never touched the cards, didn't have any kind of cheating device, and had the casino agree to every move he did.