Someone asked me this in a pretty direct way after getting a confidently wrong answer once: how am I supposed to know if what it's telling me is actually true? It's a fair worry, and there's a practical answer, even if it's not a perfect one.
For anything specific and checkable — a fact, a date, a statistic, a claim about how something works — the real answer is to verify it against an actual outside source before treating it as settled, the same way you'd double-check something a stranger told you with confidence but no credentials to back it up.
A useful habit is asking the AI itself to point you to where a claim comes from, or to search the web and show its sources rather than answering purely from memory, since that at least gives you something concrete to check rather than just trusting the tone of the answer.
For anything with real stakes — money, health, legal decisions — that verification step isn't optional, it's the whole point. For lower-stakes everyday questions, being a little more relaxed about it is reasonable, but it's worth knowing which kind of question you're actually asking.
There's no perfect way to know from the answer alone whether it's true. Building the habit of checking the important stuff against a real source is what actually protects you, not trying to detect truthfulness in the tone of the response.
If you want the slow, no-jargon version of all this — the stuff I wish someone had handed me before I fumbled through it myself — that's exactly what I built On Ramp AI for. Check it out here.