Offer Audi Dealers

Good evening together, I’m considering buying a new car Audi A4 Avant/A5. A few years ago I bought an Audi via APL (intermediate), and the transaction went without problems. Now I thought I’d write to the dealer who sold me the current car directly about an offer. He doesn’t make the percentages that APL is passing on at the moment. However, he asked me if I could register the new car via a trade, since he’s paying me €2,500. I am self-employed (individual company), but I have never used my car for the service until now. The seller told me that the registration can still run privately over me. What exactly does this mean? In order to check whether this is possible, he needs my trade license.