Here's a dirty little secret.

A lot of people don't realize it but service advisors in dealerships make a commission. And when a commission is involved, guess what? They "sell" extra services. The rationale is that "it's better safe than sorry." Many people feel that their car is a like a faithful dog and they want to reward it with a little something extra. That "something extra" is going to cost you about five tanks of gas. Your car is a machine. Your money is for you to keep in your pocket.

So why not go to an independent mechanic? This won't invalid most warranties. And once you find a good mechanic, you can talk directly to him (or her) and find out exactly what's up with your car. Service advisors never turn a wrench. They just sell stuff you might not need.

Source: Edmunds.com