Sounds like you got scammed. How could he just change the amount for the ride? Isn't there a meter that's visible to both of you that shows what's due? If he insists that you have to pay more than what the meter says, tell him to get bent.
The meter said 100, but after I tried to manually enter a tip other than 20, is when I found out about it "actually being 150". He claimed that he had turned the meter off at one point and was actually doing me a favor he wouldn't have done if he had known I was going to barely tip him. I would have stood my ground (having to give turn by turn to your cab driver for 20 minutes is hardly tip worthy), but being in front of my house I didn't want to cause a scene and was tired from my flight.
The irony is that I actually was about to take an über x quoted at $70, but I decided on a cab last minute (wish I hadnt).
I feel ya on not keeping it real every single time, but sometimes, you gotta be like, look man, it's what I'm going to pay, or it's nothing, you choose.
