My T's and Pdocs weren't in the habit of making lots of mistakes, certainly not things I would consider mistakes. Does that mean I always agreed with them? No, but I don't consider disagreement about things necessarily mistakes, just points for consideration (or no consideration). That's up to me. But honestly, with therapists, they weren't in the habit of giving advice (like punch your friend in the face -- was that serious or facetious?), so it wasn't much of an issue.

Actual mistakes? Errors in treatment. Errors in management of their practice. Errors in their approach. Just stupid judgment. I wouldn't give much grace to those kinds of errors with any paid professional.