My blog on the Internet focused on fuel injector service
Chains hire only licensed and certified mechanics. Plus, the more employees a shop has, the more likely it is to have a specialist for each part of the car, which means the shop is more likely to be able to diagnose unusual problems and to have someone who can do difficult and highly specialized repairs. The third reason is convenience. An independent mechanic's warranty on his car repair is usually good only at his own shop. If you're caught away from home, what good is a warranty for a shop a hundred miles away? On the other hand, national chains cover the country, so you would have to be someplace exceptionally remote to be more than a short drive or tow from the nearest branch of a chain where your warranty is good.