Proverbs 14:5

In the administration of justice much depends upon the witnesses, and therefore it is necessary to the common good that witnesses be principled as they ought to be; for, 1. A witness that is conscientious will not dare to give in a testimony that is in the least untrue, nor, for good-will or ill-will, represent a thing otherwise than according to the best of his knowledge, whoever is pleased or displeased, and then judgment runs down like a river. 2. But a witness that will be bribed, and biassed, and browbeaten, will utter lies (and not stick nor startle at it), with as much readiness and assurance as if what he said were all true.

— Matthew Henry's Concise Commentary (public domain)

A faithful witness, &c.--one tested to be such. utter lies--or, "breathe out lies"--that is, habitually lies (Pro 6:19; compare Act 9:1). Or the sense is, that habitual truthfulness, or lying, will be evinced in witness-bearing.

— Jamieson-Fausset-Brown Commentary (public domain)