Let's do a snap poll. Who here gets their car serviced at the dealership, and who trusts an independent shop?
While I really like this whole dealership experience (Coffee, wi-fi, hot chicks as receptionists, car wash, etc...) they tend to make you pay for it. Indie shops may or may not offer any of this but they usually are much cheaper. I also think that within their limited range of service, they work even harder to get your business.
As I don't like car payments sucking on my paychecks, I drive old cars which are fine being serviced by an off-brand shop. It's just that after moving house I had to find a new one I could trust. Seems like I found one. We talked about preventative maintenance and he turned down a few of my requests as being a waste of money.
That's how I would a define a good mechanic, but what's your definition, and where do you take your cars with a job you can't do yourselves?