They are not always right but are only RARELY wrong. And no poll ever had Kerry winning SC; you’re thinking of Ohio maybe.
The polls were also wrong on a Senate race in NH a few years back where they called it for the Rat when Bob Smith (R) really won re-election. Other than that the exit polls are almost always right.
Not, I definitely remember the EXIT polls (not the actual polls) calling South Carolina for Kerry at 5:00 PM Eastern time in 2004.
It was a lame attempt by the media to depress voter turnout further west. Some claimed they were only exit polling democrat women in South Carolina.
Of course, the state went for George W. easily.