62:12 One may not keep inaccurate weights and measure in his home or business, even if he doesn't actually use them. Doing so violates the Biblical injunction "You may not have a large weight and a small weight in your bag; you may not have a large measure and a small measure in your house (Deuteronomy 25:13-14)." One may not even keep a false measure for use as a bedpan since others may not be aware and it may eventually end up being used in business. However, if there is a local convention to only conduct business using measures that have been marked with some accepted symbol, which this inaccurate measure is not, one may then keep it in his home.
62:13 If a person wants to buy or rent something, whether it's real estate or movable goods, whether from a Jew or a non-Jew, and a price has already been agreed upon, if another customer swoops in and acquires it out from under the first person, he is considered an evildoer. On the other hand, if the price has not yet been agreed upon, it is perfectly acceptable for another person to purchase the item in question at a higher price. We are not permitted to encroach on another person's rights of priority when it comes to in renting of houses and such (see 62:18).