When your car is damaged, you have to take it to the mechanic. If insurance pays for repairs, the appraiser determines how much will be paid and the time it will take to repair it. There are computer programs that determine both values.
What happens when there is a discrepancy between the mechanic and appraiser in terms of time and money? It will not affect you as a customer except that the delivery period could be set back (but not always).
What if you disagree with the appraisal? You can hire an independent professional to assess the repair again.