It's decided by the customer and the company.
And it depends on what insurance company I decided to go with, what deductible I picked, the make of the car, how old it is, what the repair costs in my locality are, what side of the bed the adjuster got up on, and what my accident record is.
Even then, sometimes I can work out a better deal by paying cash, and keeping the insurance company out of it. Or, as I have often done with beaters I've owned, by simply ignoring the damage if it's cosmetic.
These decisions and variables will not be exactly the same for any two fenders in America.
This is real economics. Not an assembly line--an ecosystem.