The prohibition of “Ona’at Mammon” forbids merchants from selling products for a significantly higher price than the standard market price. In Parashat Mishpatim (Shemot 22:20), the Torah introduces a separate obligation forbidding overcharging a convert (“Ve’lo Tilhasenu”). Although this is in any event forbidden, as the Torah prohibits overcharging any Jew, a separate prohibition was issued with regard to a convert, due to a convert’s unique condition of vulnerability. As a foreigner with no family support, a convert can easily be taken advantage of, and merchants might be tempted to capitalize on his vulnerability and overcharge. The Torah therefore issued a separate command forbidding overcharging a convert, in addition to the standard prohibition of “Ona’a.” As discussed in regard to the previous Misva, the Sefer Ha’hinuch explained the Torah’s special prohibitions regarding treatment of a convert as intended to accustom us to restrain our natural instincts. It might be very tempting to take advantage of a convert, and the Torah’s prohibition helps us develop our power of self-restraint by requiring us to refrain from taking unfair advantage of the convert. This Misva applies at all times, in all locations, and to both males and females. A merchant who overcharges a convert has transgressed this prohibition, but he does not receive Malkut because he returns the money he unfairly charged, and any prohibition which can be rectified is not punishable by Malkut. The prohibition of “Ona’a” applies only to “Metaltelin” – moveable objects, as opposed to real estate. One who overcharges for a piece of property is not in violation of this command. The standard prohibition of “Ona’a” applies only to overcharging a fellow Jew committed to religious observance. The special command forbidding overcharging a convert, however, applies even to converts who act sinfully, due to the unique sensitivity and consideration that is required when dealing with converts. The laws of overcharging depend on the amount which the merchant overcharged the customer. If the price was less than a “Shetut” (one-sixth) above the standard market value, then the sale is valid, and the customer cannot bring any claims against the seller. If the price was precisely a “Shetut” above market value, then the customer can claim the excess money he paid from the merchant in Bet Din, but he cannot demand the revocation of the sale. If the price charged exceeded the market value by more than a “Shetut,” then the customer is able to demand that the sale be annulled. If the customer explicitly agrees to pay a significantly higher sum than market value, then the sale is valid, even though the price exceeded the market value by more than a “Shetut,” since the customer expressly agreed to these terms. He cannot then demand the sale’s revocation. The laws of “Ona’a” apply only to commercially sold merchandise. If an individual is not a merchant, but sells personal possessions, he may charge any price he wishes, and he does not violate the prohibition of “Ona’a.” When an ordinary person sells his possessions, it is expected that he does so to earn money and raises the prices well above market prices, and so the prohibition of “Ona’a” does not apply.