Ah ok - Channelling (or inspirational speaking) is a light form of trance where the person speaks words that are given from what they term "spirit" - interestingly when I was last in India I learnt about Heart speakers, a similar thing where a person would speak in a spiritual fashion.
In contrast, a Trance medium experiences a much deeper state and then a guide will speak through them. Trance mediums say they are taken away and the guide uses their facilities to speak and answer questions etc....
I would say this human dowsing thing is something that should be overseen after a period of development in a recognised circle....but you know stage hypnotists always have plenty of volunteers. There is evidence however these volunteers experience problems following the event, with insomnia and sometimes mental health problems.
Best avoided methinks.........................