mediums are a completely different thing, as they peddle a 'wonder product'. claiming things without proof and asking for money. but that modus operandi is not restricted to non-science. radioactive underware was a thing...
i am talking about people who did experience something and how they choose to interprete that experience for themselves. if you ask me, it was most likely their body and mind being pushed across certain borders - which made them feel things that where not actually there. if you asked me about my grandfather, i would tell you that he is most likely not here or there and it is just my imagination. but it gives me a little bit of comfort to at least allow the possibility that he is somewhere.
those are all personal choices about personal experiences, which do not affect anybody. but if someone start selling a product or even a religion. they crossed a line and are (trying) to affect other people.
why would anyone spend time to disprove mediums (if not for the fun of it)? like anything in science I have to prove MY hypothesis. so if a medium wants to claim what they are doing is actually ghosts, the burden of prove is on them.
i would claim, that a reasonable person would attribute the medium (not a ghost summoned by the medium), if they are seeing things, hearing things, whatever a medium does... while they are in the room with that medium person. again, the medium needs to prove anything happening is not just them messing around. i guess they could put some LSD into my coffee before leaving and make me see things alone. but i am pretty sure the LSD would be detectable and the person responsible for drugging me arrested.
a medium and other trickery cannot be used as explanation for those people who experienced the third man factor. while it is totally OK for you or anybody to say "{...}, and that’s where I would stop, I can’t explain it, I don’t know what this is.". the scientific approach would be to form a hypothesis, and start doing experiments to either prove or disprove the hypothesis. the problem is, that i cannot think of an ethical way to do such experiments. which is why, i don't believe we will be able to prove or disprove such a thing. so let's go with Occam's razor and prefer the explanation where people hallucinate things, due to body and mind being pushed beyond limits.