This proverb repeats chapter 18:8. The repetition is best explained by recognising the organisation of the book into themes, and interpreting each saying in the light of the theme in which it is found.
Let the one who hears an unjustified evil report be alert to recognise what he is hearing, and let him be impartial in rebuking the gossip. There are times when we must declare what evil others have done, but even then we need to scrutinise our own motives. We may be called to witness before a duly recognised authority, to give evidence at a trial, to expose a serious wrongdoing, but we must search our hearts to see if we are governed by bias, prejudice, revenge, jealousy, or hatred. We must report what we saw or heard with strict accuracy and with no exaggeration. While the day of grace continues, we must seek the good of others, and hope where possible for their repentance rather than their condemnation. Above all we must not give sly half-truths, designed to create prejudice in the hearer, by playing on the partiality which we know already exist in their hearts, by manipulating the weakness of fallen human nature. We must encourage others to come to a true judgment, just as we should come to a true judgment ourselves. As we should speak in this way, so we should insist that others speak to us in this way.