Casinos will alter the used cards before they are sold or given away to prevent cheaters from buying them to cheat at table games.
One of the common cheating ways is card marking. Many casinos, particularly those in Las Vegas alter the decks of cards they sell to tourists – either by punching holes through the middle of cards or trimming their edges – to prevent cheaters from returning to the game tables after buying the cards and then slipping the favorable cards into their hands when playing.
How the casinos drill a hole in the middle of the cards? It’s a small and regular hole. It is said that after the cards are used. They are gathered by security and taken to a room and destroyed by drilling them and in some cases. And someone also said that probably it’s just an old tradition that nobody remembers the reason for that nobody bothered to change. But I am more inclined to believe that casinos drill holes in the center of cards and/or cut the corners off of the cards that’s because they take out of their regular rotation to prevent cheating.
After being drilled or cut off the corners, the used playing cards are sell as souvenirs in the gift shop https://www.invisibleinkmarkedcards.com/marked-cards.shtml, or donated to non-profit organizations. Any cards not sold or given away are destroyed, usually incinerated. The same things happen to the dice.
People who have worked on casino said, the average life span for a deck of cards or a pair of dice in a well-run casino is about 4 hours. You may think it would be a huge cost if the change the cards and dice every 4 hours, but take the dice as an example.
Dice will become worn down on the edges from being thrown by the players, and also become oily. Anything that can affect the balance of a die or its randomness must be avoided. But it’s not cost-effective for the casinos to try to repair damaged dice, they are tend to change it other than repair it.
That’s the reason why the casinos deface their playing cards and dice.