I have a friend of a friend of a friend etc.
But, even without shadowy connections, you can get access to the Black Book
Black Book Auto | Home
It aint cheap -- wait until you are ready to buy a car, have financing set etc. This is only something you need when you are ready and able to buy.
In a pinch, NADA Yellow Book is a good alternative. KBB is really only useful if you are selling a car, trading in (to prepare for the screwing to commence...), or looking to buy from a private seller. It is not especially helpful for buying from a dealer (for starters, it presumes YOUR car is Average to Good and THEIR car is always Excellent and flawless...).
Edmunds and a few other online trackers can give you a ballpark on what the given car is going for in your area, but that only helps you to get screwed no better or worse than other folks (assuming their reports are accurate...)
The other stuff is strategy (e.g., don't be afraid to walk the **** out) -- and yes you have 100% of the leverage, because the worst they can do is not sell you the car. It's not a rare artistic masterpiece, its just another machine working its way to entropy.
All the Black Book does is give you a clearer picture of the absolute lowest you can even haggle for. It gives you a legitimate lower bound to start with and it defuses their ability to point gleefully at the MSRP, like that number means anything.
Of course, no matter what you pay, you are screwed, because essentially all cars are money pits and lose value steadily from the time it rolls off the lot. Strategy, patience, Tony Montoya fortitude, and some knowledge mitigate the depth of the initial screwing.
Note: None of this will work as well if you are in a situation where you need a car ASAP... then you have less leverage, obviously -- just don't telegraph that to the seller...