In poker there is the rule that cards speak, which means that no matter what you say when you flip over your cards, you actually have the best possible hand you could make. For example, a common miscall in holdem would be if the hand looked like...
...and you flipped your cards at the showdown and said, "I've got a pair of aces." Because cards speak, you would not be held to it. You actually would have two pair, aces and sixes. Two pair would be the strength of your hand, despite your minor blunder.
Most public cardroom rules include a cards speak rule. The exception would be in certain games of Lowball. There also may be some crazy variant that may not use the rule but in any authentic casino poker game, your miscalls are covered.
It's the responsibility of the dealer (if there is a dealer) to point out that a hand is miscalled. However, any player at the table, in the hand or not, can identify a miscall. It should actually be each players' duty to point out if a another has miscalled a hand.
It is important to note that the cards speak rule does not carve out exceptions for cheating. Namely we're talking about deliberately miscalling a hand to induce other players to reveal their hands. It is mentioned often in many poker rules that a player who intentionally miscalls a hand will automatically forfeit the pot and be given a warning. If it is done again, that player could incur a time penalty (if in a tournament) or even be removed from the game.