Well, it has finally happened to me today. I was quoted an up-front fare, and they charged me a lot more than that. I did screenshot it, but the imbeciles at their customer service department have tried to tell me that the drop-off location was different (It was not) and that my total was "within the estimate." If I'm quoted an up-front fare, that's all I've agreed to pay.

Don't worry, Uber apologists, I did tip the driver.

What a joke. Time to initiate the dispute with Amex.