"Our credit lines are accepted at over 1,000 auctions and accessible with other inventory sources throughout the U.S." and "Use your AFC line of credit to finance customer trades, dealer-to-dealer transactions and purchases made from auctions, leasing companies and other sources." This is how these services are being used.
And I'm not saying they won't eventually have to account for that inventory financially, but the process moves so quickly (at least at successful dealerships) that the dealer's bank statement will probably never even take the hit for the vehicle, because it's acquired and sold within weeks or days if they're buying the right inventory for their customers. The ones who aren't go out of business.
You're conflating independent used dealerships with franchise new dealerships who also happen to sell used cars.