Both doctors and mechanics deal in arcane lore, and then charge people for their services based on their arcane lore. Sadly, the process and price some times are blended in such a way as to milk the sheep, so the wariness of one snake oil salesman for another may not be that surprising.
As to professors and Mechanics, one of my best engineering professors in the Mechanical Engineering Department, Professor Keith, was also a shade tree mechanic. In his life, by 1978, he had owned two cars. The station wagon he was driving when he was my advisor was at the time 17 years old, maintained solely by himself. His encouragement to me in that regard was what got me to buy a VW , as my first car, and not a Camaro, and to fix it myself. My dad was a 'buy it, take it to the mechanic at manufacturer's recommended intervals, and budget for the cost' kind of guy. Not enamored of cars and axle grease, he preferred woodwork and gardening.
I wish, to this day, that I had progressed to body work and never let that car go. I'd rather have the money back from the other cars and still have the 1974 Super Beetle, now that I have been through it all.
Oh well, we don't make every correct decision in this life.