" Echoing his teacher, but using many more words, St Thomas Aquinas began his analysis of just prices by posing the question ‘Whether a man may lawfully sell a thing for more than it is worth’.53 He answered by first quoting Augustine that it is natural and lawful, for ‘you wish to buy cheap, and sell dear’. Next, Aquinas excluded fraud from legitimate transactions. Finally, he recognized that worth is not really an objective value – ‘the just price of things is not absolutely definite’ – but is a function of the buyer’s desire for the thing purchased and the seller’s willingness or reluctance to sell, so long as the buyer was not misled, or under duress. "

― Rodney Stark , Reformation Myths: Five Centuries Of Misconceptions And (Some) Misfortunes