When you order pizza from the menu:
Is it customary to expect extra-toppings to be free?
Is it customary to tell the chef that the cooking time is too long?
Is it customary to play the restaurant off against the pizza parlour down the road?
Is it customary to negotiate the hourly rate of staff with the restaurant owner to lower the price?
Most puzzling: why are these customs default practice when trying to build a relationship with your supplier?