From imdb.com:

Revealing mistakes: Cruise ship poker dealers are certified professionals, however, the Poseidon dealer allows both "splashing the pot" (thowing chips directly into the pot) and a "string bet" (placing chips into the pot as a call and then placing more chips in as a raise). These are basic rules violations of professional dealing and would never be allowed in a cruise ship casino, especially in a high-stakes game such as the one in this movie.