A good mechanic will tell you "it's $800 to fix the transmission, if the rotors are bad it'll be $1300." and if he finds is estimate is way off, that's his fault so he will take that on the chin and do right by the customer. Same for contractors who work on your home, sometimes you accidentally bid under cost and learn a lesson for next time.

Hospital estimates in the rare case they are provided only seem to get revised in one direction, that seems like having cake and eating it too. If the high school drop out painter can live by his estimates, so can the national hospital chain full of Harvard Business School graduates.