It really depends on the dealership. Crevier will mark-up the sh!+ out of a M car, but it's negotiable, I was told by one of the SAs there. Riverside also will mark-up the car. Steve Thomas in Camarillo? I don't know, but I seem to remember reading that they don't. Don't quote me, though.
The point is that you need to shop around. Talk to all the dealers. A longer drive to a dealer might net you some savings. Don't generalize one dealership's or SA's practice to all dealers/SAs.
E30 1991 318is, Red on Black Leatherette
Family History: Two E21 320i, One E28 535is, One E34 535i, One E34 540i