Electrician Service Call, Come with me and Replace a Doorbell, what it looks like, Thoughts?

I installed a new doorbell this customer's home for $300. This took me about 15 minutes to complete. As an electrician, you pay for my years of experience, not the time spent. So, a customer called and said that their current doorbell was cracked and they could not press it anymore due to weather and age. I undo the two mounting screws with my Phillips screwdriver, then I undo the current doorbell wiring. There are only two wires on a doorbell with two screw terminals. Typically, one red wire and one white wire. I'm doing this live. It doesn't matter which terminal each wire goes on. You can put them anywhere and it'll still work. These wires are tiny 18-gauge carrying 12 volts. Not enough power to get zapped, so no need to turn off the power. And boom, we just finished. They not like us and they not like us. I put my tools away, customer satisfied. He even gave a $25 tip. I put that right in my pocket and that is what a day looks like as an electrician.