"If the customer is wrong, they're not your customer any more."
This is going in a review deck I'm working on for next week.
I agree that when you treat a customer like they're wrong, they'll walk away from your product and tell two friends, and they'll tell two friends... you get the picture. You only have so many chances to help a customer out, and turn around their perceptions. And if you don't, you risk alienating them.
Seth is worth reading regularly.