What does Proverbs 29:12 mean?

God created everything which exists; that which is true corresponds to His creation. In the same way, that which is good corresponds to His will. Falsehoods and lies contradict both God and His creation. So, dishonesty is not merely immoral, but also undependable. A good ruler seeks truth and has no time for liars or flatterers (Proverbs 16:13; 20:6; 25:5; 29:5). When a leader tolerates deceit, liars will rise to power and eventually all his advisors will be corrupt (Proverbs 14:34; 28:16; 29:2). Rulers risk being overthrown by unscrupulous counselors or being killed by invaders if they rely on the advice of immoral men. A ruler who naively trusts lying counselors is likely to render false verdicts when his subjects come before him in civil and criminal cases.

Fortunately, Solomon (Proverbs 25:1) was a just and wise king, who rendered correct verdicts.

Someday Jesus will be king over all the earth. He will not listen to lies and false accusations. Isaiah 11:2–4 promises, "The Spirit of the Lᴏʀᴅ shall rest upon him, the Spirit of wisdom and understanding, the Spirit of counsel and might, the Spirit of knowledge and the fear of the Lᴏʀᴅ…with righteousness he shall judge the poor, and decide with equity for the meek of the earth."