there is huge margins for a 7er at dealer(well actually any of their cars)...roughly 10k. i would go by VMR pricing and go from there. VMR doesn't take into account condition of car but you should be within a grand or so of VMR pricing. just like purchasing a new car I always negotiate by how much of a mark up vs how much of a discount i get off their stated price.
if you are watching for a 2006 750i at BMW CPO - on Tues evening Autohaus listed a 06 750 for 37k! next day they replaced the price with 47k. opps...i think someone put in the wholesale price by accident.
shame i didn't take a screen shot of it.