It's easier with new cars than old cars because you have an apples to apples comparison. The problem I had with using carwoo is that even after negotiating the price down, showing up at the dealership they tried to add in all these extra bullshit costs.

I think carwoo operates by users paying a fee like $200 or so, and is free to dealers. Dealerships treat it as a source for qualified buyers. carwoo also gives you some basic reviews of the different dealerships and car pricing info based on your inputs.