And whence is it derived that one should not be precise (in weighing) in a place where an "extra" is generally given (to the customer), and that one should not give an "extra" in a place where it is customary to be precise? From (Ibid. 15) "a just stone shall there be unto you."
And whence is it derived that if one said, in a place where it is customary to give an extra: I shall be precise (and deduct the amount of the "extra" from the price); or, in a place where it is customary to be precise: I shall give him an "extra" and deduct something from the price or add something to the price — Whence is it derived that he is not heeded? From "A whole and just stone shall there be unto you." And whence is it derived that (grain) is not heaped where it is the practice to strike it, and that it is not struck where it is the practice to heap it? From "a just ephah (measure) shall there be unto you." And whence is it derived that if one said, in a place where it is generally struck: I shall heap it and add to the price; or, in a place where it is generally heaped: I shall strike it and deduct from the price — Whence is it derived that he is not heeded? From "a whole and just measure shall there be unto you."