 In the case of commercial transactions, particularly of necessities, the late scholastics recognized legitimate charges for mercantile services of transportation, storage, and risk-taking, but condemned the practices of price gouging and other types of market manipulations, particularly the forestalling, regrating and engrossing of grain supplies. As for singular purchases of land or a luxury item, Aquinas unpacked in considerable detail the question of whether or not it was ethical to sell a good for more than it is worth. Notwithstanding customary prices, he recognized numerous circumstances where this might prove not only legal but also ethical. While berating the Roman maxim of caveat emptor, he endorsed the prevailing principle of laesio enormis which stipulated that the contracted price could fall within a fifty percent range (plus or minus) of the customary price. The doctrine of the “just price”, one that covered costs but was also sensitive to local conditions of demand, was further developed in this period and is still at the core of commercial law. Aquinas also reviewed four different contexts that would permit the charging of interest. One articulated the concept of an opportunity cost, and another appealed to the arrangement of capital transfer known as a partnership still honored today by Islamic authorities. Increasingly, commercial loans saw the principal as a form of capital that had legitimate and alternative yields. In sum, the late scholastics offer many insights on commerce and trade, the status of the Crown in managing legal tender, and the inherent tensions between commerce and virtue.