Eyes on the car/buy/buy

Hello, my topic has to do in a different context with security, but I don’t know where else to go with the thread. To my problem: I am currently offering my car at autoscout and mobile. Yesterday I received a call from a buyer – as far as possible. We quickly agreed. I stumbled on a condition that the buyer addressed. He asked me if I kept him in writing in the purchase contract, about 1 month after handover for the function d My question to you now, is this common? It seems to me Spanish… The car is currently a company car and I can identify the VAT. So much for it. Thanks in the VOrraus, roc