Confession was made compulsory in 1215 at the Lateran Council. Confessors became a kind of regulators, providing advice and inflicting fines, called “restitutions”. Merchants and traders became their main targets and restitutions a sizable source of income for bishoprics and monasteries. Peter Olivi created price theory to show that their concepts of ‘just price’ and ‘usury’ were misconceived and harmfull to the ‘common good’. The paper brings out his path-breaking contributions using the language of elementary microeconomics, culminating with capital-asset pricing and long-distance trade. It then highlights the salient thinkers that kept his legacy alive across about three centuries.