You shouldn't overcharge your patients.
Alex is a mechanic, and his next customer isn't really knowledgeable about cars.
Alex has to figure out what to charge his customer.
Alex only charges the customers what they're supposed to be charged.
Alex makes up problems that the car and charges double what they should've paid.
The customers are more than willing to pay for it since it's not that much money.
The customers end up paying the mechanic because they need the car.