Mediumship is now more commonly called channeling.  The semantic difference between the two words may be that mediumship is generally limited to contact with the dead. 

      A channel is not just a radio through which information is broadcast. The channel often adds much "color" and bias to the information.

     Do not think that, by virtue of not being in a physical body, the entities being channeled are totally enlightened beings.  Just being dead does not make one wise!  There is no guarantee that everything coming through a channel is always 100% accurate.

     You should question and not accept any material coming from a particular entity until that entity has proven itself to be accurate and helpful.

     More often than not, channels who are not conscious of their channeling, are more accurate than conscious channels.  But this is not always true and no channel is 100% absolutely accurate.

     Often the person consulting a channeler suspends all judgment and rational thought along with their disbelief,  ending up in more of a mess than they were before they consulted the channelller. 

     Another unfortunate effect of believing these things is that when, inevitably, the channeled material turns out to not have been so perfect, the ensuing disappointment can lead to completely giving up on consulting channelers or on reading channeled material.  Disgruntled, the disappointed person  swears to never again put their trust in a channel or psychic.

     Obviously, there must be some kind of middle ground between having so open a mind that it is virtually empty and having a mind that is completely closed to the idea of channeling and to the information that can come through a good channeler.

      There is.