Car sales to a vehicle intermediary

Hello together, I am about to sell my Golf 7 R at the moment and got a call from a father with his son on Friday. You would like my car and they would have a friend who owns a vehicle broker who would clarify everything for them and get the car. He called today and inquired about the car, offered me a deposit & the rest of the amount cash at pickup and would also get the car with red numbers. As far as everything was good (the colleague I could Now my question: Is there anything I have to pay attention to? With whom do I best conclude the contract and should I keep in the purchase contract that the buyer has switched on the vehicle brokerage? I would still notice that I sell the vehicle privately and also not be liable for the costs of the intermediary (you can never be sure enough).. Does anyone else have experiences with such a thing or tips? Thank you! Greeting Ersin