Flattereth - literally, "The man who opens his lips," who has no reticence; such a man, with or without intending it, does the work of a talebearer.

He that goeth about as a talebearer revealeth secrets,.... Or, "he that revealeth secrets goeth about as a talebearer"; a man that has really got the secrets of others out of them respecting themselves and families, and the affairs of them, or however pretends he master of them; goes about telling his tales from house to house, to the great prejudice of those whose secrets he is entrusted with, or pretends to be; and to the great prejudice of those to whom he tells them, as well as to his own; this is contrary to the law of Moses, and the rules of Christianity, Leviticus 19:16;
therefore meddle not with him that flattereth with his lips; or "mingle not with him" (g); do not associate with him, do not keep him company, have nothing to say to him or do with him; for when he flatters you, and highly praises and extols you, he has a design upon you to get what he can out of you, in order to expose you elsewhere; therefore suspect him, be upon your guard, shun him and avoid him. It may be applied to false teachers, and their deceptions with good words and fair speeches; the word used signifies to deceive with the lips; see Romans 16:18; and well agrees with the parasites of Rome, Revelation 18:23.
(g) "non miscebis te", Pagninus, Montanus; "ne misceas te", Baynus, Mercerus; "ne admisceto te", Junius & Tremellius, Piscator; "ne commiscearis", Michaelis; "ne admisceas te", Schultens.

Those dearly buy their own praise, who put confidence in a man because he speaks fairly.

Those who love to tell news will hardly keep secrets.
flattereth . . . lips--(compare Margin; Proverbs 1:10).
meddle . . . him--literally, "join," or "associate with."

19 He that goeth out gossiping revealeth a secret;
And the babbler have nothing to do.
Luther otherwise (like Hitzig) -
Be not complicated with him who revealeth a secret,
And with the slanderer, and with the false (better: loquacious) mouth,
so that ל and the warning apply to the threefold description, a rendering which Kimchi also, and Immanuel, and others at least suggest. But in connection with Proverbs 11:13, the first line has the force of a judicium, which includes the warning to entrust nothing to a babbler which ought to be kept silent. Write גּולה סּוד, as found in Codd. and old Edd., with Munach on the penultima, on which the tone is thrown back, and Dagesh to ס, after the rule of the דחיק (Gesen. 20, 2a), altogether like קונה לב, Proverbs 15:32. 19b the Venet. translates after the first meaning of the word by Kimchi, τῷ ἀπαταιῶνι τοῖς χείλεσι, to him who slanders and befools, for it thus improves Theodotion's τῷ ἀπατῶντι τὰ χείλη αὐτοῦ. But פּתה means, Job 5:2 - cf. Hosea 7:11 - not him who befools another, but him who is befooled, is slandered, by another (Aben Ezra: שׁיפתוהו אחרים), with which שׂפתיו here does not agree. But now he who is easily befooled is called פּתה, as being open to influence (susceptible), patens; and if this particip. is used, as here, transitively, and, on account of the object שׂפתיו standing near cannot possibly be equivalent to מפתּה, the usage of the language also just noticed is against it, then it means patefaciens or dilatans (cf. הפתּה, Genesis 9:27, Targ. אפתּי = הרחיב), and places itself as synon. to פשׂק, Proverbs 13:3; thus one is called who does not close his mouth, who cannot hold his mouth, who always idly babbles, and is therefore, because he can keep nothing to himself, a dangerous companion. The Complut. rightly translates: μετὰ πλατύνοντος τὰ ἑαυτοῦ μὴ μίχθητι χείλη.