It is no different to the fact I couldn't tell you whether my GP is any good or not - It is little more than blind faith that when they give me a prescription to take to the chemist is actually going to treat my condition. Same goes for my mechanic. I think he is great and recommend him to everyone, but it is little more than blind faith that my car is currently roadworthy.

For what it's worth, it's fairly well-establish that for GPs being nice goes much further than being the best in your field in avoiding malpractice complaints. For any lawyer having to deal with laypeople, client management (being polite, listening carefully, taking an interest, finding something to like about other people and being liked yourself) is one of the most important skills.