Cheaters or conspirators use marked poker cards to gain unfair advantages in a game. The cards can be altered in many ways, including scratching with fingernails or adding invisible ink to them using pens and markers. This card marking technique allows the cheater to scan or read the back of a card from afar, allowing him to know the value.
This is a very common problem, especially in home and underground games run by people that don’t know much about poker or are just looking to win every game. The best way to protect yourself from these types of cheaters is to be aware of the different methods they use to mark cards. Some of these methods include bending the cards or crimping them, adding small marks around the edges or even cutting a part of the design on the back. These techniques can be very effective, but they can also be easily detected by other players or hidden cameras.
One of the most reliable and trustworthy card marking methods is luminous ink, which can be applied to the face and back of a deck of poker cards. Luminous ink is invisible to the naked eye and can only be detected by certain contact lenses or sunglasses that are specifically designed for the purpose. However, be aware that many unscrupulous traders are willing to sell poor-quality luminous ink to magicians and poker players in order to steal their money. You should only buy cards from card-marking professionals with a proven track record.