Argument 402: if an Employee Who Was Taking Money in Gold Coins to Pay Some Debts, Or to Make Some Purchases, Took Advantage on the Way of an Opportunity Offered to Exchange Those Coins for a Better Price, Could That Employee Appropriate for Himself the Extra Charge Obtained in This Manner?(Treatise on Money) (Excerpt‪)‬

The matter we are discussing in this argument happened frequently in Portugal when I was teaching these subjects. At the time there was an abundance of coins of 1,500 reais and debts were paid with them, or they were handed over to an envoy to be used to buy merchandise for their owners. According to what we have said, it was possible to exchange the coins with an additional benefit over the price they had been appraised for when minted, without breaking the law for it. The issue in question is whether the envoy under discussion, when knowing beforehand who was willing to give that extra charge, or looking for [that person] himself, might carry out that exchange and get for himself the extra charge using the rest of the money to pay the debt or buy the merchandise as they had ordered him to do. May he keep the extra charge or should he restitute it? And who does he owe the restitution to? The same uncertainty exists regarding the officers of the king who are in charge of collecting the royal revenue, and other ministers who carry out similar duties for other members of the aristocracy and, in general, the depositaries to whom many debts are paid in currency that they have no obligation of assessing for a higher price, and then, by order of the king, or of whomever they are ministers of, pay salaries, debts, and other expenses. During the time between the collection and the payment, these people have the opportunity to exchange the collected coins for other [coins], thus obtaining an increment, and it is uncertain whether they may keep that extra charge or should restitute it.