If you know nothing whatsoever about cars or maintenance thereof you will get taken by the salesman then you will run your cars into the ground burning money and then get ripped off every time you need someone to maintain or fix your car because you don't know enough to know when someone is bullshitting you.
People are expected to know SOMETHING about cars because they are frequently a huge expense that you are required to expend to be able to exist in a lot of places.
Econ 101 in this case assumes that time and money are fungible in any particular increments and that the money they earn doing whatever they are optimal at is greater than the cost of the specialists services.
Example someone making 20 bucks an hour needs a professional service that requires 3 hours of work for a professional at a cost of $900 learning to do so ineffeciently for 5 hours then spending 6 hours seems like a, huge waste but consider.
- Just because their labor is worth $20 an hour doesn't mean that they they can trivially in the context of their current obligations convert a day off into extra pay right when they need it.
- 11 hours x 20 hours will furnish 1/4 of the money required. Even given an immediate alternative it will require 45 hours of additional work.
Incidentally if you own a home you probably ought to learn at least enough basic maintenance to fix simple things.
This is often effecient in practice.