Resignation of purchase contract / water damage

Hello, together, in October of last year we acquired a hobby Prestige 610. As it turned out, the part of core scrap. Have had an expert report carried out by the Dekra, where it was finally written broken. Lawyer is turned on, lawsuit runs. The seller has praised the caravan as very well and in a super condition. We also believed that without further ado because he has a bill of a caravan workshop about the testing of the WW as well as a fresh HU of the TÜV Rheinland which he passed without defects. Now my question: How can this be? How can a workshop and the TÜV overlook such gross damage or wave through? Nobody does anything like that… The papers look real. Is the quality of the construction of the WW even HU relevant? Questions about questions. I’m pretty sure that we have the right on our side and one can blame the seller for such malicious deception. Only this HU report wurds me. The seller calls on this now and gives away from the massive water damage that ultimately led to total unusuality. Of course, I don’t know anything about their experience about the TÜV.