Trust Assuming an agent with some semblance of what is often called a "mastery" of one's native tongue...
When we place trust upon another to tell us about the world and/or ourselves, we expect sincerity. That is true for everyone. We expect them to believe what they say.
Some however also expect truth. On my view, that sort of expectation is no different in content than expecting another to form, have, and/or hold nothing but true belief. The problem, of course, is that everyone forms, has, and/or holds false belief at some point in time. So...
Omniscience is not required for honesty, sincerity, "telling the 'truth'", and thus trustworthiness. It is clearly unreasonable to expect otherwise. None of us are omniscient. Not one. Not any. All of us are not.
It follows from this reasonable, and still yet readily attainable, criterion for "truth telling" that...
Truth is not necessary for trustworthiness.
What sense does it make then? Well, sincerity is all it takes. The speaker must only believe what they say as well as believing that they've said all that's relevant to the matter. The takeaway here is that the very idea and/or notion of "telling the truth" conflates truth and belief or demands omniscience. Neither is acceptable. That's shameful - to put it mildly - given the influential power of it's use.
Truth is presupposed in all thought, belief, and statements thereof somewhere along the line. Telling the truth is simply stating all that you believe to be relevant to the matter at hand(whatever it may be).
The truth, the whole truth, and nothing but the truth...
...is an impossible criterion to satisfy at face value if everything said must be true. People could go to jail for saying exactly what they believed to be the case, simply because they expressed false belief. They would be convicted and sentenced for perjury simply for holding false belief, if counsel could convince the juror of perjury for giving false testimony, for not telling the truth.
Thus, to continue to expect any individual to always say true things shows an emaciated understanding of how thought and belief work. No one can do that.