The Auto Broker I dealt with simply maintained an office with staff. I'd call and explain what I wanted (exactly) and how far I'd be willing to drive. Then his research staff would query using their software/national data base to see what was available within the parameter I was willing to travel.
Within a week or 10 days after talking with him I got a call from him telling me where the car was and the price. He asked how soon I could be there and told me how to bring the payment. (Bank Cashiers Check from my Credit Union) I had the Treasurer/Manager's business card attached to the check so all they had to do was make a call to authenticate the check.
I paid a fee for the service to the Broker and that was all. His firm did not finance, insure, or in any way involve themselves with the transaction other than that. It was a hold over from the year before and this new car was greatly discounted from it's original price. The purchase was outright (no Trade in BS) as these kinds of transactions tend to be cash and carry. The NADA Book value of the car which had 23 miles on it was was well below average loan value. It looked like it had just arrived at the dealership new.
What I'd suggest to anyone is to Google for Automobile Brokers (state by state). There are loads of used car lots calling themselves brokers, offering finance, with photo galleries of what they have in stock. Chances are that you are just dealing with a Used Car Salesman at these websites.
You need to find a Broker that "locates" vehicles for you based on about what you are willing to pay, an exact description of what you are looking for, and how far you are willing to travel to pick it up. You'll be advised of the payment method, to get an Insurance binder from your Insurance agent, (to transport the vehicle so it will be covered in the event of an accident), and any extras. (this may include taxes, title/Manufacturers Certificate of Origin, temp tags for transit home etc.)
But such Brokers can find new and used in about anything you would want. (in used they may inquire of how many miles you would find acceptable)
But this is what you could expect going through a Broker. Then, you may consider an extended warranty program that would pay for any breakdown, towing, or parts.