The 3 times I’ve bought a new car or truck, I told the dealership to not put anything on the car, like their decal. My first new car in 1987, I told ‘em that. They were surprised but complied. All 3 places honored my instructions.
True, all one has to do is ask them and, from my experience, they will comply because 1) they want to make the sale and 2) for every person wanting no decal or dealer advertising on their car there are hundreds who didn’t think of having the decal or advertising removed and are driving advertisements for the dealer.