I don't personally understand the appeal. While some dealerships are certainly sketchy, I've found high-volume traditional dealerships to be pretty straightforward. They price them to sell, you pay the price that's posted on the sticker/website.
Financing is financing. It's not the car. If you show up without knowing how you're going to pay for the car, well... you showed up without knowing how you're going to pay for the car.
Yeah, they'll ask about extended warranties and such, but it's just a matter of saying "no" a couple of times while signing paperwork.