One day a school psychologist who I know told me, "How much should you tip your school psychologist?" It was a rhetorical question. School psychologists are not traditionally tipped, and earn a salary for their highly educated expertise. This is paid by the school, which has an interest in the well being of their students, who are not expected to pay. A psychologist would, of course, appreciate any additional funding.
The French have a joke about "Déformation professionnelle," a pun on their term for professional training. When all you have is a hammer, the entire world looks like a series of nails. This leads to bias. Most professional people tend to view their profession as the most important one in existence. Things tend to go downhill from there, as people attempt regulatory capture to favor their (naturally all-important and perfect) industry.
Perhaps this is a reason not to listen to me. My specialty is computers, and I try to make my advice as practical as I can, but some of my interests are probably useless to the average person.