As always, you're offering great advice and insight.
There are probably more shops that are trustworthy than not. I expect that the independent shops are more likely to be so because they have no other source of revenue to fall back on, such as new car sales.
Unfortunately, it doesn't take too many bad ones to cause people to be leary and skittish. Add to that the fact that no shop is completely infallible. With the best of intentions a technician can replace or rebuild something only to find out that it did not correct the problem. The customer that has been burned somewhere else, then believes that the honest attempt at correcting the problem was some sort of ripoff. I believe that in most cases, given the opportunity, an honest shop will somehow make good.
If a customer gets to know the shop and what they're about, in the long run, they will be most satisfied.
Unfortunately there are those shops out there that prey on people. In the course of selling a '96 E300D, a lady who had wrecked her MB asked me to drive her to her independent mechanic. He gave the car a quick look, gave her his approval of the car and then began telling her how it would require the same service as her previous MB. He said it would need brake pads every 12,000 miles and brake rotors every 24,000. I was appalled. First of all, unless she rides with her foot on the brake, this should not be necessary. Second of all, how can he recommend this as a preventive maintenance item. I was really suspect of him.
As Steve says, get to know the shop. Although good shops have to start at some point in time, a shop that has been in business for some time would be a good place to start.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in