הלכה על שבת 61:11

You should be extremely careful not to deceive your fellow man. If anyone deceives his fellow, whether a seller deceives a buyer, or a buyer deceives a seller, he transgresses a negative commandment, for it is said:¹Leviticus 25: 14. "When you sell something to your neighbor, or buy from your neighbor, do not deceive one another." The first question a person is asked when he is brought before the [Heavenly] Court is: "Have you [always] been honest in your dealings?"²Shabbos 31a.