Shop keeper simulates an open market economy each "day" it randomly pairs a shop keeper and a customer. If the cutomer finds the price acceptable they will perform a "purchase" for that price and the shop keeper will attempt to raise the price. If the price becomes unacceptable the customer will no longer purchase the item and the shop keeper will drop the price. Since the system is closed with a set number of shops and customers the price will find a stable point that both find accpetable.