How do you know if someone who says they are trans is actually "cis"/not trans? How do you know, if you are not sure, if you are "cis"/not trans after all?

How someone answers this question will say a lot about how they think about gender.

There is the interesting inverse question of someone "in denial": do you think this is possible? If so, can an outsider know that a person is "actually trans" if they insist that they're not? How?

Do you think there's a clear answer? Do you think a doctor can know it-- how do they find out? Do you think a person who is questioning can know it-- how easy is it to know? Do you think friends or family could know it about someone in their lives-- what clues them in?

If you think there is a clear answer, did detransitioned people know the answer while they were transitioning? (Why did they transition anyway?) If they didn't know the answer, why is it that some people don't seem to know?

Every trans person knows of some trans person that they suspect isn't "really" trans. What's up with that person? Do they know-- or not -- that they aren't trans? If they don't know, should someone let them know? Why or why not?

Can you do a test to find out? What would that test involve? How would the test prevent false positives (identifies someone as trans, who isn't) and false negatives (says someone isn't, when they are)? Would it be harder to prevent one than the other?

How accurate does the test need to be in order to be a good test? Who should be in charge of the test- a doctor? (What kind?) Who should it be given to, and why? If someone thinks they're a false negative or positive, how could they prove that?

If you were an average Jo(e) & suspected someone was lying about being trans, how could you find out if they were lying or just an unusual example? What would you look for to tell you? What could you say to someone else to prove to them that that person was faking or lying?

If someone was fooling themselves into thinking they were trans, how could they eventually figure out the truth? Is there anything someone else could- or should- say to them that would help? Is it something you have to figure out by yourself- why? How do you do it?

Is there any condition or life experience that looks a lot like being trans, but isn't? How similar is it? How do you tell the difference between an "actual" trans person and the other? Can you- or the person in question- tell the difference before someone decides to transition?