Do those fixed price dealers count their various add-ons (rust proofing, extended warranty...) in the fixed price or not. These add-ons are how most dealers make money (that and warranty work)
Whatever is on the sale sheet is included. You can order extra stuff, they will install it for you, but obviously it’s not included in the advertised price.
Honest question, when the customer knows you're trying to fleece them and is willing to pay a small premium to finish the deal and get on with their lives, why would a dealer double down on something so outrageous?
Basically if scamming your customers works a nontrivial fraction of the time and the margin when you're not scamming is small, scamming is the incentivized behavior.
Obviously there could be bad dealership which would try to screw you, read some reviews and don’t go to such place.
Beyond that, their advertised specials are spectacular deals usually. Who spends money and attention advertising specials that don't even compete with the competition?