damages

Happy holidays
How do you calculate damage to a vehicle, for example a scratch? Do you calculate how much it costs to repair the damage or do you calculate how much the vehicle was worth before and how much after? The dilemma is that I remember there is a Ḥazū’ that says that when a window is broken in a house, you don’t calculate how much before and how much after, but the damage to the window, and to me it is similar to a Ḥad. And perhaps it is obligatory to rule according to the laws of the state.
2. Assuming that the answer is to put how much before and how much after, in case I know that this person will charge me full damages, is it possible to run away and only leave an amount of money that will cover the payment that needs to be paid?
Thank you very much, Happy holiday.