Question

Happy holidays.
How is damage to a car assessed—for example, a scratch? Do we assess how much it costs to repair the damage, or do we assess the car’s value before and after? My uncertainty is that I seem to remember a ruling of the Chazon Ish saying that when someone breaks a window in a house, we do not assess the house’s value before and after, but rather the damage of the window itself, and maybe this is similar to our case. Or perhaps one is obligated to rule according to state law.
2. Assuming the answer is that one has to assess the value before and after, in a case where I know that this person will charge me full damages, is it permissible to run away and only leave a sum of money that covers what really has to be paid?
Thank you very much, and happy holiday.