I was brought up to believe that fortune-telling and seances were wrong, so I still tend to steer clear of mediums and fortune-tellers.
However, I have had experiences that could be called seeing ghosts. I lived for years in a flat that had the ghost of a small black cat. People I had never mentioned it to, have seen it, so I don't think it can be thought transference.
The day I visited my sister for what I was fairly certain would be the last time, as she was dying of brain cancer, I distinctly felt our mother, who had been dead for seven years at that time, standing behind me in the hospital. I didn't turn round, so I don't' know if she could be seen.
It may just have been our need for her that caused me to feel her presence, of course. My paternal grandfather appeared in my sister''s bedroom, waking her, the night before our father (his eldest son) died. My sister had been so small when grandpa died, that she didn't recognise him, but when she told me, I knew who it must have been.
Once or twice I have felt my sister behind me in the street -- nonsense? wishful thinking? Perhaps, after all she died nearly four years ago.