I've seen a few companies pitch something similar to your concept. From the acquisition side my main concern is going to be when a dealer purchases a vehicle through your platform and finds out there is something wrong with it that wasn't disclosed by the seller. Who's on the hook? Or is it entirely up to the dealer to perform an inspection at time of purchase? Inspections on purchase would significantly slow down the process, likely upsetting the customer, and also lead to offers being changed once dealer inspections are performed. This leads to poor a customer experience in the customer's eyes.
I generally like the idea of a private party auction space for dealers to buy vehicles from but there are too many variables when it comes to the everyday consumer listing their vehicle for sale.