I wouldn't worry about preconceived ideas anymore.

As far as doctors go, I studied the history of science in graduate school, there are a LOT of things that people in the medical profession think was the right thing that turned out to be totally wrong or bad. I think even today with modern medicine, there is some of that around. I don't see a doctor as anything more than someone who just spent a lot of years in school, they all have preconceived notions so it is best to find one that suits your needs, not one where you suit their needs.

Health food store clerks, probably around the same knowledge base as a McDonalds employee. They are there just to sell the product, and that is probably it. Luckily I have a low carb store in my area, makes a big difference...