I certainly am not totally aware of all the official rules in live poker at a casino, but I was under the impression that a verbal declaration is binding. Two pair loses to 3 of a kind, so if a player declares 4 of a kind as two pair, would he/she not lose the hand to 3 of a kind? If that happened to me, I would ask for the poker room manager to make an official call on that.
Like detroitjunkie said,
cards "speak" for themselves at showdown, not a verbal declaration...Verbal declarations are only binding with actions(bet, call, raise, check, fold)
Always remember that verbal takes precedence over action, e.g. let's say you announce a bet of $400, but at the same time shove $800 by mistake, the bet would be the verbal declaration of $400. Conversely, if you mean to just call a bet, but shove in more than the call by mistake, WITHOUT a verbal declaration, the chips determine the bet. So, if it's $400 to call, and you shove $800 and then say "I call," you actually just raised to $800.
Hope all that made sense and actually helped lol