Guarantee excluded in the KV, is that legally valid?

Hello dear forum, am new here and have a question to the experts here… On 04.07.2017 I bought a used scooter from a dealer (a small workshop in the neighborhood) for 500€. As a student this is a considerable sum. In the last week the scooter gave a few strange sounds of itself, which is why I took him to the above-mentioned mechanic/chief of the workshop this week. Yesterday I then received a call and he said it was a motor damage (ir On my question, what can be done now and what the options are he meant only the following: “Sell on eBay or you can see if you can get the parts or buy a new engine for the model.” So…that was last night and I was at the university at the time and also talked to a few friends. It immediately fell the word “guarantee”. Especially when selling a business to a private person. I have now released the purchase contract. ucht and can give the following information: My question is now: is this legally valid AND permissible? Or do I have the right to guarantee despite these points, since it is a dealer/company and is not a private sale? It is after all a motor damage and that can not really come from today to tomorrow, I think. Of course I will go to the workshop on Monday and look for a dialogue with the gentleman so that I get the 500€ purchase price refunded. e (but he is stubborn and intransigent about this), which is why I want to know how I stand legally…