Eye contact alone is golden. With no words offered from me, the car salesman negotiated the price of our new car down and double the trade in of our old car.
I do this every time I'm buying things with negotiable prices. My trick is to not use any eye contact until negotiation time. The surprise throws most people off their game enough to give you an advantage. Plus, it is kind of fun watching someone talk themself out of money. FYI, it doesn't work every time, typically there will be an awkward silence and I'll have to throw out an offer.