My (motorcycle) mechanic quotes me based on the parts and the amount of time required to do the repair. So she'll say "A new set of tires is $130, and the shop

My (motorcycle) mechanic quotes me based on the parts and the amount of time required to do the repair. So she'll say "A new set of tires is $130, and the shop labor is $110 an hour. If you only bring in the wheels, then labor is just $50." I'm not sure what magical force is causing my mechanic to behave this way. It could be personal preference, some kind of regulatory requirement, pressure from competing shops, etc. Whatever that force is, it doesn't seem to exist in the american sickness and treatment system.