How to detect a marked deck?

This is a question that most asked. Some players who want to cheat in poker games may ask how can they read the marked decks. Some players who want to prevent being cheated may ask how to detect a marked deck as well.

How can we tell it as a marked deck when facing the marked cards? To see a not so good marked deck, you can tell it if the cards have darker back than others. Some may even have some light visible marks to naked eyes.

But when referring to a good marked deck that people can't see any invisible ink marks by naked eyes, the marked cards reader is necessary. Then we can consider the marked cards contact lenses or infrared sunglasses, which can detect the invisible ink marked decks well.