Motor vehicle replacement sum higher than the sum paid by the trader

Hello community, I am currently facing a question that I still couldn’t resolve in my mind. I currently have a Peugeot 208 on sale at Mobile.de. Today a serious dealer from another federal state who is looking for a car on behalf of a customer. The dealer is himself a large Peugeot dealer. He wants to propose several cars to the customer and asked for my data and asked for my final price. If the customer chooses my car He would pick up the car. The car is financed and in a few months the final rate would be due. This is higher than the sum that would be paid by the dealer. However, the dealer would like to have the car letter at pick-up. However, I can’t advance in the big full amount. How do I best deal with the situation. Has anyone experienced an idea or specifically the same? Thank you very much!