I am not a gambling expert, so I can't be sure if it's doable, but I keep wondering how do they know if someone using any app [or their mind] to do those allegation. Arbitrage betting, I can understand, they cross-check with other books and platforms. But card counting? They turn on someone's webcam and see if the player is frowning excessively or keep scribbling something, or perhaps get into the device's system and scan for any app running? I'm genuinely curious and would love if anyone can give me an educated guess.
They certainly count cards themselves, and if they see a player increasing his stake, or joining the game when probabilities are good for the players, and decreasing his stake or leaving the table when they are higher for the dealer, they can deduce he is counting cards. Online casinos use a large number of decks generally and only deal half of the shoe to prevent players getting a positive EV by counting though.
