Big chain "service" stores have mass and momentum behind them and it's "their way or the highway" for the most part. They play the numbers and don't really care if you do business with them or not. Plus, they always seem to find a way to not honor prices, warranties, etc. I run a small business and will ALWAYS go the extra mile to try to make a client happy. I want their business and I want them to recommend me to other potential clients. My goal is to make it easy to do business with me. Not necessarily so with chain service stores. I get a lot of business from pissed off ADT clients. A LOT.
That being said, I have found Pep Boys to be a little pricey, but they have done excellent work when I've had to use them.