One may not keep dishonest weights and measures, even if one never uses them: Bava Metzia 61b
Storing one's weights in salt: Bava Metzia 61b
If partners wish to divide land, measuring for one in the winter and for one in the summer, with a rope which is vulnerable to seasonal shifts: Bava Metzia 61b
Measuring out liquids and including the foam at the top: Bava Metzia 61b
Beyond the Laws
One must always make certain that his "Yes" and "No" are honest: Bava Metzia 49a
The greatness of honesty and trust in Gd: Taanit 8a
One who falsely claims his assets belong to another party, to avoid appearing rich, will complain in court and they won't be able to help him: Bava Metzia 75b