I always tell them ahead of time - no decals and then if the are on there tell them they have to take them off - now get me another cup of coffee while I wait. ticks me off
I once told the dealer that in order to have their decal on the car I was buying they would be charged $20.00/mth. for advertising. When they prepped the car it “miraculously” no longer had the decal and instead had a dealer license tag frame, which I threw away when I go home with the car.