snip
I definitely was prepared to walk
away, but the subtlety of the leaning-in tactic is great.... I would never
have thought about that one.

I had a boss that always tried to be higher than whoever he was
negotiating with. For his guests in his office, he had an overstuffed
armchair with a stiff, uncomfortable back. When you sat down in it, you
would sink low. Whenever I needed to have the upper hand, I would sit on
one of the chair arms, like you might do if you were only going to be
there for a minute. This placed my head well above his, and you could
tell it threw him off. After a while he replaced the chair with an
armless one, and wouldn't sit down until after you did.

lean in = control
folded arms = closed attitude
open arms and legs = open attitude

Experienced salesmen know body language, and some can tell from this
that even though you are saying no, there is still room for negotiation.
Start with open, friendly body language, and when you are putting your
foot down, do just that. Put your feet flat on the floor and fold your
arms. That will reinforce to him that there you are not giving any more
ground. It never hurts to check your watch now and then, either. It
makes them worry that they are going to lose you.