While there's no way to ever determine the truthfulness of a poll, this is the time of the year when polling firms have the greatest incentive to be as accurate as possible. They know that soon people will be measuring their last few polls leading up to the election against actual results.
The polls in 2000 were terrible. They had Bush in a landslide. I think it depressed Republican turnout.
No matter what the polls say, the election will be determined by turnout.