I used truecar (through overstock.com, I don't think overstock uses them anymore though) 2 years ago to buy a sonata. It was a great experience, and quite a lot off sticker.

Zero negotiation, walked in with the paper, that's the price of the car.

I don't think you will get the deal of the century through them, but you'll at least not get screwed. Just don't let the dealership nickel & dime you on protectants & floormats, etc. If they can't honor the exact price, just go somewhere else.

On the flip side of the other comments, I used the TrueCar service about 4 months ago. For the specific trim that I wanted (standard trim, not crazy options), several dealership websites had prices on them that were several thousand dollars lower than the TrueCar price, and that was before any negotiations happened at all. So I would use the TrueCar service again for doing research, but I am not confident of their ability to deliver a good "no haggle" price.

I bought a car a couple months ago, and as soon as the sales manager saw a TrueCar page open on my phone, the negotiation ended and I paid the price on the phone. Pretty amazing how easy it was.

Their website says "Negotiation Free"