My BMW 4 series was backed into while parked by a nice neighbor , I was quoted 4000$ for repair. He initially said he would settle with cash. But the body shop recommended using insurance as repair will take few days.

I was planning to sell the car before this incident. Carvana offered 18000$ for the car. Since the neighbors were nice I said we will work with them on what ever makes it comfortable for them.i am worried the car value would go down with this.
2 questions
1)
Should I get the car repaired or keep the money and try to sell the car with Dent in the door.
2) if repairing should I go with his insurance or take the cash from him?