I could not get better rate, because I’ve never had credit card. Even despite my clear and sound mortgage history, the bank doesn’t give me good rate. Many sleeky dealers start to explain about different pricing bs and different "dealer fees" etc...
You must understand me that hitting one dealership like that I dialed Mercedes Benz customer service to file a complaint and the rep herself advised me to call factory direct and shared her personal experience.
A call to factory direct sales got me a free airfare ticket and hotel stay for a week for the starters just to feel the difference instead of hustle here in our beloved USA.