"A trustworthy witness will not lie, but a false witness utters lies"
This is another in a whole series of bits of wisdom that seem to be business wisdom.
Notice the verse above this one about oxen or multiplied effect with equipment and personnel. Also notice the one after this which involves a scoffer and then a fool in the verse after that. Solomon is trying to school the young, the young at heart, the naive, and those who have not learned yet. A person who is trustworthy will not lie even if it is to their advantage.
So if you want to find if a person is trustworthy, ask the question: Do they lie to save their own skin or benefit their position? The implication is to hire the trustworthy person and do not hire the false witness.
This proverb is an understanding proverb. It is trying to help you build a connection between things that you might not normally make: lying and lack of faithfulness; truth and steady faithfulness. These are linked, Solomon says. One of the obvious personal applications is: Are you trustworthy? Most people would say "yes." But this proverb asks the question: Do you lie to save yourself or to enrich yourself? If you do, then there is also a trustworthy issue. If a person cannot be trusted to make personal sacrifice for the truth, then there is not enough of a commitment to truth.