With humans, it is often easy to establish who hallucinates and who doesn't. We can all identify a snake oil sales pitch. However, with LLM, it can often be a lot harder.
Let's take an example. I studied physics and can likely answer most questions on nuclear physics. However, as it is a while back, my answers will not sound as smooth, and I may have to correct myself a few times.
If you ask ChatGPT the same questions, it will come up with elegant, convincing answers. As a layman, you will likely prefer what ChatGPT comes up with, as it is answers are eloquent. Of course, until you build a nuclear reactor using ChatGPT knowledge. Once the fuel rods become critical and start making its way through the earth's crust, you may realise you should have relied on my stumbling answers instead.