I can tell chat bots aren't real when they answer too quickly. They never make spelling mistakes, but do subtly mess up language pragmatics. This is the written ones.
I think I could agree that they might be "real" if they somehow only felt like they "aren't from around here," but I haven't even felt that they even get that close.
One big tell is that spoken conversation often circles around on itself where you ask the same question but in slightly different ways. Humans who are honest respond with consistency but slightly different wording.
If you keep hearing the exact same phrase, ie. "That's understandable." and especially with the exact same intonation, then you've got yourself a bot.
BTW, technology has gotten better. When humans speak a string of numbers, the last one has a downward intonation indicating the end of the sequence. I remember when voice robots would not do that. Now, they often do. Pay attention to it the next time you get stuck in some phone response tree from hell. It'll take your mind off the frustration.
Another cue that you're not talking to a real human is when you curse them out and they reply cheerfully, " I can help you with that!"
Real people hang up on you!