Plinko

For example, there is a Card counting method in Blackjack that aims to give the player an edge over the casino. While card counting is not illegal per se (as it relies on mental acuity and strategy rather than external devices), it is generally frowned upon in casinos, both physical and online.

Most casinos reserve the right to refuse service to card counters, primarily because it undermines the house edge and could potentially lead to losses for the casino.