Car rental purchased?!

Good day, since I have a lot of problems with my 2.5 month old used car (see https://www.motor-talk.de/…/…gen-wasser-im-kofferaum-t6688609.html) today I was allowed to leave my car at the workshop again. Since I was planning a week’s workshop stay for the repair, I got a rental car from the car house. I drove home with this car and when I took a look at the car, something seemed familiar to me: KENNICHING. the last two digits differed, with my vehicle standing in appearance with the previous owner, which was also the car dealership. For example, the sign of my car: ABC-DE-520, that of the car rental jett ABC-DE-560 So slowly I can explain to myself where the many defects of my car could come from. But now to the actual question: must be stated when selling, whether the vehicle was a rental car? I mean with taxis that must be done (?!) in the end a rental car is nothing else, only that the car is driven even by several people. Greetings