I would agree that the Paypal adress is pretty binding, BUT only if the buyer requested it. I've seen posts here (and experienced it) where sellers say they send their paypal address when someone requests a shipping price, to save time (ie: "Shipping would be X, making total price Y. My paypal address is XYZ"). That in my mind doesn't count as binding, if the buyer only requested a shipping estimate and the seller just adds in their paypal as well.