There can be physical phenomena such as levitations. I know one medium who has poor eyesight and wears glasses, but his Guide in trance can see perfectly. If you go to a trance session and are not convinced, don't assume that all Trance Channelling is the same. Also, the phenomena can vary from session to session even with the same medium. Spiritualists know that conditions can have a lot to do with it.
All mediums do best when conditions are very good.
Even the best mediums can do poorly if the conditions are bad. The best trance work is done in a good circle. A Good circle is made up of people who get on well together. It is harmonious. The circle is happy.