Merchant wants to sell payment in the customer order. Risk?

Hello her, when buying a new vehicle my old vehicle was given in payment. Now the dealer asks whether he can sell my old vehicle in the customer order. Does this mean a Riskio for me? I know that the dealer is fine as a result of this regarding guarantee. What if after the purchase of my old vehicle a defect occurs and the buyer then turns to me, since the dealer has sold in the customer order.