Earlier quoted context omitted.
(b) you can change your tip afterward if your service was not as expected. Just like in a restaurant: maybe your default tip is 25%, but great service bumps that up, and bad service bumps it down. You go in expecting to pay 25%.
We bought a second car at the weekend, I phoned up my insurance company and asked them to put it on. They did so, and it was cheaper than the quote I'd got online - £180 for 9 months vs £290 for 12 months. So I immediately tipped the person on the phone £45 How ridiculous does that seem?
You're comparing apples and oranges. Tipping is just the way portions of the food service industry works.