ANSWER:

As long as the damage doesn’t exist anymore and it is as good as new, you don’t need to tell about it and the profit is halal. 

QUESTION: I bought a car with damage, i repaired the car and sold it with $2000 profit. But i didnt tell the customer who i sold the car to that the car had damage in the past. Even though i repaired the car, am i still sinful for not telling the customer about previous damage? If im sinful, what is the sin? Does this make the $2000 profit into haram money?