You're really misunderstaning the power balance here: when you go to a doctor or a dentist you are not a customer buying their services, you are a supplicant be

You're really misunderstaning the power balance here: when you go to a doctor or a dentist you are not a customer buying their services, you are a supplicant begging for their mercy :) That's why they work the hours they find convenient, and you have to go through the hoops to make it on time for your appointment. This logic however does not apply to barbers.