Payment Mercedes.

Hello to you. The following facts: Two weeks ago my girlfriend bought a Mercedes A class in a Mercedes branch 180km away. I got it with her and because I also played with the thought that it will be time for a new car, I asked if I can give my payment and what I get. Is an Opel Astra J 2011 1.4 Turbo 110,000km. I told him that he has scratched the bumper at the back of a wall (about 20cm x 3cm big scratch), S I don’t know anything else. He wrote it all down, copied the vehicle license and said that it would go abroad anyway and he would report with a price they would pay. In the afternoon the call came and he meant we would give you only 3000€, I know little but more is not in it. I then said that it is ok and he has the financing contract for my the selected vehicle is finished. There it says: Buyer gives his old vehicle in payment: 3000€ and the chassis number. Now on Friday the pick-up of my new one and the Astra I give you. At the beginning of the week we had a short phone call and I asked once like this is actually, they have never seen the car, if the 3000€ then already fit. On that he said: If you did not hide an accident or was leased somewhere, then it fits already, you have two Aut yesterday we made another phone call because of the time on Friday and he meant that one of dekra still sees my Astra and if the car is rated lower I have to pay the difference to the 3000€ on it. Why don’t they look at the car in front of the whole? Contract is signed by both, there is, as said, customer gives vehicle in payment 3000€. Can he then even ask for anything at all? There is nothing that the car is still being checked etc. Should they really demand something else this is for me boldest attempt to push the price still. What do you think about it?