It is forbidden for a person to keep a deficient measure in his house or in his shop, even if he does not measure with it. If he does keep [such a measure] he transgresses a prohibition, as it is said (Devarim 25:13-15): “You shall not have in your bag weights, a large one [for measuring what you buy] and a small one [for measuring what you sell]; you shall not have in your house measures, a large one and a small one, a full and just weight shall you have, a full and just measure shall you have…”.’ Even to make the measure into a chamber pot for urine is forbidden, as perhaps someone will comes who doesn’t know and measure with it. If there is a local custom that one doesn’t measure except with a measure that has been marked with an official mark, and this (pot) is not marked, one may keep it (at home).

We already mentioned this point in Rashi’s name a few times. The prohibition is even just owning the tools for fiscal dishonesty; even with no intent of being dishonest. The “just in case” of someone perhaps being misled should be considered too evil to risk.