I couldn't tell you. It's one of those rare times where the cliche stock image or portrayal of a salesperson tends to fit the overall experience. I swear that the only reason I get good deals is because the dealership Ive gone to made a couple of mistakes with us, and my wife is better at their game than I am. I don't have the patience that she has.
First time, I went to their dealership when my gas gage died in an '03 Civic. They had to replace my whole dashboard, resetting my odometer. We reminded them when I was trading it in to get my wife a '12 Oddessy. They valued my Civic much higher due to that, then when they realized the issue, they tried to reneg on the deal. "You didn't tell us that it actually has more milage." Well, here's the place where your mechanic put the sticker. Here's the info we updated in our handwriting, correcting your information when you first made your offer. And, if you looked in your service computer, all the info on the car's history is there as well. They weren't happy.
With my '19 Ridgeline, where we were trading in our '06 CRV, my wife just walked in and said "here's what we're looking for, and I don't want to pay any more than (X amount), make it happen or I'll go somewhere else.
Most people are taken for rides, and I don't see many dealerships that try to erode the perception of the "shadey car dealer," as you point out.
Car ads themselves are simply always the milage it gets and the monthly rate for cost (radio ads). Television ads are only the car driving on a smooth road (insert season here), then depending on the type (SUV, Truck, sports car), you see basic stock videos of it doing what the consumer would want out of it.
When shopping around, we were going between either the Tacoma or the Ridgeline, and one would think that Honda would advertise the greater leg room in the backseat of the Ridgeline. I had to sit in both trucks to find that out. My kids are growing, so it was a point of interest for us.