Is it acceptable for a player to have marked cards in their deck if they do not have sleeves?

In Magic: The Gathering tournaments, having marked cards in a player's deck is not permissible, regardless of whether or not the cards are sleeved. Marked cards can give a player an unfair advantage as they can easily differentiate between the cards based on their markings. The integrity of the game relies on the level playing field created by ensuring that all cards are indistinguishable from one another, which is why clear card sleeves are often required in competitive play.

When a tournament official discovers that a player has marked cards, the appropriate action is to issue a Warning. This serves as a reminder for players to keep their decks in compliance with tournament regulations regarding card marking and to take steps to prevent it in future games. Thus, it is essential for all players to keep their cards in conditions that do not compromise their uniformity to maintain fairness and the rule of law within the game.