Kitzur Shulchan Aruch, Rabbi Shlomo Ganzfried
Chapter 62 : Laws Concerning Business and Commerce
Anyone who gives short measure or weight, even to a non-Jew, transgresses a negative commandment as it is said: "Do not falsify measurements, whether in length, weight, or volume," (see Ch.182:1, 4 below). The punishment for giving short measure and weight is very severe, as it is impossible for a person who gives short measure or weight to repent properly, since he does not know how much and whom to compensate. Even the active participation in communal affairs is not considered suitable repentance.
It is written: "You must not keep in your bag two different weights, one large and one small. You must not keep in your house two different measures, one large and one small. You must have a full, just weight, and you must have a full, just measure..." The words "your bag" and "your house" appear to be superfluous and our Rabbis, of blessed memory, explained: "You shall have no money in your bag." Why is this so? Because you had different weights. "You shall lack the necessities of life in your house." Why is this so? Because you had different measures. But if full, just weight is in your house, then you will have money; and, similarly, if full and honest measure is in your house, then all your needs will be filled. Furthermore, our Rabbis of blessed memory said: "What should a man do to become rich? He should conduct his business honestly and ask for compassion from the One to Whom riches belong," as it is said: "Mine is the silver and Mine is the gold."
You should measure and weigh generously. [That is,] you should give more than the exact quantity, as it is said: "You must have a full, just measure." What does the word "just" imply? Says the Torah: "Be just by giving him some of your own."