Commentaire sur Le Lévitique 25:17

ולא תונו איש את עמיתו YE SHALL NOT THEREFORE BE EXTORTIONATE TO ONE ANOTHER — Here Scripture warns against vexing by words (wounding a person’s feelings) — that one should not annoy his fellow-man, nor give him an advice which is unfitted for him, but is in accordance with the plan and the advantage of the adviser. But lest you should say, “Who knows whether I had any intention to do him evil?” Scripture therefore states: “but thou shalt fear thy God”! — He Who knows men’s thoughts, He knows it! In all cases where it is a matter of conscience (more lit., a matter handed over to the heart), when no one knows the truth except the one who has the thought in his heart, Scripture always states: “but be afraid of thy God”! (Sifra, Behar, Chapter 4 1-2; Bava Metzia 58b; cf. also Rashi on Leviticus 19:14.)

ולא תונו, the reason this is repeated so many times is to warn you that you must not even misrepresent by words and thereby treat your customer unfairly. Even if the damage caused is not measurable in terms of money, all manner of misrepresentation is forbidden.

ולא תונו איש את עמיתו, "And you shall not take advantage of one another." Baba Metzia 58 explains that our verse discusses אונאת דברים, "verbal wrongs." The plain meaning of the verse is that seeing the Torah had already issued a similarly phrased commandment in verse 14, and we had explained that commandment as applicable when overcharging for chattels, we could have thought that overcharging for land was permitted. The Torah therefore had to repeat this commandment in connection with land sales so that the reader would not err and assume it is permitted to overcharge on land. The verse therefore concludes with the exhortation: "you shall fear your G'd," telling us that although the normal legislation against overcharging does not have a legal effect when the sale of real estate is involved, this is so only in connection with land sales in the rest of the world and to members of society at large (Gentiles). The prohibition to overcharge is in effect, however. The reason there are no legal repercussions when someone overcharges for the land he sells is that G'd personally will exact the appropriate penalty from the guilty party; this is why after the words: "you shall fear your G'd" the Torah adds the words: "for I am the Lord your G'd." G'd reminds us that He Himself will judge us in this respect and that we must not assume that it is permissible to overcharge when selling real estate. There are many instances of the Torah forbidding something without making such prohibitions a matter punishable by our legal system. You may do well to read what I have written on Exodus 21,12 in this connection. In our specific case, a court might find it difficult to determine precisely when the seller has violated the rule that he must not overcharge, seeing a purchaser may have been willing to pay more than the market price. (the same applies if the buyer bought the property for less than the market price, exploiting the economic weakness of the seller). G'd alone knows where to draw the line between what a buyer is truly willing to pay and what he feels he is forced to pay. This is why G'd Himself will administer any penalty due to either of the parties involved.