Buying contests

Hello I have a question and it would have been a problem for one already 6 weeks ago I had my brakes changed in the car dealership and where I paid a salesman came to me and asked if a 5 doorr would not be better for me because I only lead a 3 doorr and with child was stupid I said yes would be better and he offers me one to I wanted to have still to think about time because I didn’t have so much money then 2 weeks later I wanted to listen more carefully what the m i can offer everything and there he wanted mine for the red because he made me aware that there were cracks in my compartment and suspects that there was a hail damage and that the previous owner only repainted and spat was I told him that all the windows were renewed and the roof was repainted he wanted but nevertheless mine offered me 6000 for mine that I only have to pay on 3800 euros I agreed and changed the car ever he has me called and said that the roof is completely fucked up and completely a new one has to be on it therefore he wants to challenge the purchase contract or I pay 3000 so that the car corresponds to the value again because my car is not because of that 6000 value but I can not see under the paint as loan and knew that also he can not challenge the contract although he knew that the roof had scratches? Because I want to pay .net I know yes .net if he fucks me because he when buying contract k a flaw has written though I have told him everything ps. I drove my old car only 1 year I hope you have an answer