I tried with my last car, MB Carlisle were pulling out all the stops to avoid doing a deal.... They let me test drive a dirty, ill-prep'ed car which needed a bundle of "we'll fix that before you collect it" work done. Then they offered me bottom book for my 211, minus £300 to tidy up a small scratch on the paintwork, as a trade-in against top retail book on the car I wanted to buy. The 'salesman' then went off to his manager to see if they would move on the price... he offered to drop the price on the car by £200.... on a £24k sticker price... I walked straight out.
The dealership was like a ghostown all the time I was in, I wonder how they stay in business... I wasn't looking for a giveaway but I was looking for some sensible prices to change... a price I was able to get elsewhere without trying. The MB warranty bit isn't worth the extra thousands you pay to buy the cars there... I still got £1500 worth of work done by MB under warranty on my 6 year old car despite not being bought from an MB dealer.
Just out of interest (and sorry for going off-topic), when were you in MB Carlisle? Recently?