Gaming

The character knows most common games of chance and skill, including cards, dice, bones. draughts. and chess. When playing a game. the character may either play out the actual game (which may take too much time for some) or make a proficiency check, with success indicating victory. If two proficient characters play each other, the one with the highest successful die roll wins. A character with gaming proficiency can also attempt to cheat, thus gain a +1 bonus to his ability score. If the proficiency check for the game is 17 to 20, however, the character has been caught cheating (even if he won the game).

Paladins

A paladin whose ethos includes moral objections to gambling will not engage in games of chance. Using this proficiency to cheat is a serious ethos violation.

[Player's Handbook]
[Complete Paladin's Handbook]