Garage Cabinets, Garage Storage, and Garage Organization

I currently own a 2008 535i in perfect condition with leather,sports pkg,auto,and ipod intergration and I'am looking to hopepfully do an even trade with a dealer for a 07 mercedes packaged similer. My car has 15,000 miles on it which is alot for an 08 but  its a popular car right now that a dealer would have no problem unloading. My Question is would it be feasible to think I would be able to trade my car evenly for a 07 merc E-350 without having to pay anything? Do dealers even do trades like this? I know I would get more money for it if i sold it privatly but then I wouldnt see the benefit of the tax deduction from the mercedes since i would be buying it outright. Does anyone have any insight or advice on my situation????

Thanks alot for your help.  

Dealers buy low and sell high, is the first rule. A BMW is worth more at a BMW dealer, than at a Benz store. If you look at used car web pages there are three categories private sale, trade in, and wholesale, go from there. Sales tax is an atvantage, depends on what the trade value is, and what a private sale can bring.