I see what you are getting at now, Katnip & yes, I agree.
By and large, I do think people think they see things that they then call "ghosts". I don't think they are all liars, but I do think a lot of embellishment goes on when they are relating their story later.
We all do this all the time. Ask any police officer.
I dismiss the notion that ghosts exist. Completely.
I do not, and never have, dismissed the idea that people think they have seen ghosts. But to be fair, most "ghostly encounters" are so bloody stupid, that yes, I do dismiss them.
Few of them are: Grandma came back & talked to me for half an hour (those are rare).
They are more like: "I was in the kitchen & felt cold. Suddenly the cat hissed and the curtains flapped. Explain that then".
Do I dismiss the second example as crap? Oh yes.
The first, I would be kinder and suggest they see a doctor.