Stop in for a cup of coffee

What's everyone's rule of thumb for breaking off a sale negotiation?

I hate selling stuff to begin with... so my patience is very low.

Price + the ride
Offer
Counter offer
Agreement
Agreement, but with me paying shipping

I'm done... now I kinda don't trust you
Some people have more nerve than a wisdom tooth. I see something i want, make one offer within reason.
Lowballers are the worst to deal with, i send em packing.