Cases in which you SHOULD NOT!  see a medium.

If you feel you are impressionable, if you are still in a grieving process,

If you feel you are not able to keep your distance and to actively continue with your life. If you are looking for a psychiatrist and you would rather need a good therapy. If you are of the impatient type of personality and want that everything comes to you as you snap your fingers and in the blink of an eye. If you think that the medium practitioner is a magician and he/she can boost your wishes, it is simple:
DON´T MAKE ANY APPOINTMENT !
Conversely, if you are «able to listen, to take notes, to manage the information as it is presented and you can consider it as it is – with some distance and discernment -.If you are endowed with analytical capacity and your character is benevolent and open, then you can book an appointment.