I guess advertisers think we are all f***ing stupid

What really frosts my balls is when going to a dealer, and looking at a vehicle and it has a "market adjustment" sticker price. Saw one a few months ago that had a MA price 30% over sticker MSRP. Are people really stupid enough to pay this ripoff? How about the "dealer fee"? I went shopping for a late model used car a couple of years ago. agreed on price and had the sales person write up the contract. The first thing I did was cross out the $850 dealer fee. I was told that is added to every sale. Said "not this one" and got up and walked out the door. Before I got out the parking lot my phone rang "we can waive that charge" come on back. There were a couple of other things where I got what I wanted, by my willing to walk out the door. If you can't get the deal you want, be willing to walk away. Even at the end, when paying. The dealer said they couldn't/wouldn't accept payment using a credit card. I got up and walked out the door. The next day I was back (after they called) and used two "cash back" cards. When the card statement came, I did a balance transfer to different cards that had no interest for 18 months, and the cash back of the first cards equaled the transfer fee. So free financing for 18 months.
What law says you have to buy on their terms?
I worked at a dealership for a dozen years (not in sales) and the last thing the sales staff want's to see is you walking out the door. That instantly puts you in charge of the sale and they sure don't like that. I lost count of how many times I heard the sales manager say "don't let them walk". As a buyer, that's the best thing you can do.