Change chance in case of a hidden deficiency

Moin moin together, I’m new here because someone advised me to make a contribution here. I just describe what happened and hope for help… I bought a car a 3/4 year ago that made one or the other problems a few weeks after the purchase. I tried to have the defects fixed close to time. However, a deficiency did not get better even after 2-3 repairs. Now I had the faxes thick and wanted to sell the car quickly again. it is clear that I do not get close to the price I paid again and that after a few months…. Now I tried to give the car in payment. At the same time the car was rated by the TÜV. An expert then told me that the car at some places starts to rust (this lack was known to me). However, the reason is that there was leased and repainted, so the expert said, it could also be that the car had an accident (in the purchase contract there is accident At least, however, it is a hidden defect that was not displayed when buying. According to the expert, a reason to change the vehicle. I have addressed the seller to it.. he told me that I must have had the accident… I of course did not. Now I ask myself, if I take legal steps and the seller (dealer) simply claims that I had the accident… can he get away with it? The expert s agt “yes”… to my question whether the corrosion could determine the approximate time of this “accident” he denied. Well, right and right is the well-known game… What can I do now to get right? Has any of you already had experiences with such a story?? Can any of you give me a tip on what I can do?