“Unequal weights .” Unscrupulous merchants often kept stones of different weight in their bag that only they could easily tell apart so that they bought a lot and sold a little. But that kind of dishonest dealing is an abomination to Yahweh (Lev. 19:35; Deut. 25:13-16). [For more on trading using honest balances, see commentary on Prov. 11:1].
“are not good.” This is the figure of speech, tapeinosis, “understatement.” False scales are not just “not good,” like unequal weights they are an abomination to God.