I used to work with a chap who changed his van every 18 months and told the dealer any stickers and he didnt want the van as he wasnt going to give free adverts on his van, if they want to put their name on it they should pay for it.
got my new van home, it was in the sun and the sticker just lifted off easily, the factory sticker on the inside of the front window however has been more of a fiddle to get off without soaking!!!