Praise be to Allah.
There is nothing wrong with you taking the sum worked out by the manager of the showrooms, because this matter can only be decided by people with experience. The basic principle is that the one who causes damage to someone else’s car is liable for the damage he caused, in addition to the loss of value of the car as a result of the accident.
It says in al-Mawsoo‘ah al-Fiqhiyyah (1/226): We do not know of any scholarly difference of opinion regarding the fact that in the case of damage, if the item damaged is something that could be replaced, the one who caused the damage is liable for its replacement, and if its value can only be estimated, then he is liable for its estimated value. Similarly, we do not know of any scholarly difference of opinion regarding the fact that with regard to estimation of the value, attention should be paid to where the damage occurred. End quote.
It also says (28/233): There is no difference of opinion among the fuqaha’ regarding liability for loss of property as a result of it being usurped, damaged, or destroyed entirely, and the like, whether that damage was done deliberately, by mistake or out of negligence. End quote.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: The issue is not the issue of replacing the damaged part of the car; rather it is the issue of replacing the damaged parts and also the resulting drop in value of the car as a result of the collision. This is something that many people may not pay attention to, but everyone knows the difference between the value of a car that has been in a collision, even if it has been repaired, and the value of a car that has never been in a collision.
End quote from Fataawa Noor ‘ala ad-Darb
Based on that:
There is nothing wrong with you accepting this money, even if you are able to get the car repaired for less, because of what we have mentioned about the necessity of taking into consideration the drop in the value of the car as a result of the accident.
There is also nothing wrong with you keeping your car, or selling it for scrap, in addition to accepting this compensation.
And Allah knows best.