Unequal weights are an abomination to the Lord,
and false scales are not good.
Just thirteen verses before there is an almost identical proverb: "Unequal weights and unequal measures are both alike an abomination to the Lord." Perhaps the repetition is to reinforce the seriousness which God attaches to cheating.
Consider this proverb with the one preceding it: "Do not say, ‘I will repay evil' wait for the Lord, and he will deliver you." Have you been cheated by unequal weights and false scales? Wait on the Lord. You see how he regards such offenses. He will deliver you. Justice will be carried out in exact measure to the offense of the crime.
Do not take matters into your own hands by trying to out-cheat the one who has done you wrong. Do not try to even the playing field. The cheater will eventually be exposed. Even if he is not exposed as timely as you desire, know that God sees all and works all for your good. The cheater will receive his due reward.
Your focus needs only to be on doing what is right and honest. Do not act in reaction to evil doers; act in response to your righteous Judge and Lord who desires to see righteousness displayed in your life.