I work with a guy who, for a flat $950 fee, works with me to find cars at auction.
I know *exactly* what I'm paying if I buy a car from him.
He's a regular dealer. This is a service he offers. He finds a car that meets your specs, helps you understand if you want that specific one, and if you do you pull the trigger. It's yours. From that point on it's just another dealership sale that he works. The sales paperwork has only a few lines: auction price, transportation (if any), his fee, sales tax, title/doc fees. You know all of those going into it before you pull the trigger.
The car comes into the dealership a few days later, and you all get to look at it to make sure it's the car you pulled the trigger on. Not just the VIN; you also get to agree (or not) that it matches the auction description.
His job is to be the middleman between you and the auction--and he takes responsibility for the car meeting the auction's description. If it doesn't, he works with the auction to rectify the situation to your satisfaction--anywhere from doing reconditioning all the way up to sending it back. If it doesn't meet the auction's description, you're off the hook.
It's a nice way to buy a used car. The best way to leverage this is to buy one with factory warranty left, and then buy the factory extended warranty (if the factory offers such a thing).
This is why the CPO market came about--it helps bring people into dealers, and makes them competitive against a situation like this since the dealer can take an out of warranty car and sell it as CPO.