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
Buyer always pays shipping it's his stuff now. He got your original price down and now wants you to pay shipping too?? BS!! If he really wants it, he'll pay.