This is what has always been drilled into my head: You are not only being paid for the job, but also your education, experience and tools..
That being said, if you can do the job CORRECTLY in half the time the additional time you are paid is for your know-how of being able to do the job quick and right, or for some variety of uber expensive tool that allows you to do it fast..
When I have a customer bark about being billed an hour for something that took me 10 mins to do I ask them to do it themselves in an hour, or I ask them if they have the thousands of dollars or tools to even begin to do the job.. The tune usually changes, or they don't come back.. And anymore I don't get too upset if those particular few don't come back. Of course not every tech is in the position to do such shenanigans...