The trait of PRIDE in mediums:  
“All moral imperfections are so many open doors, giving access to evil and ignorant spirits; but what brings us
most often under their influence is pride, because it is the defect which of all others, we are least apt to recognize
in ourselves.”

“Pride has been the ruin of a number of mediums endowed with the highest faculties, and who, but for that defect,
might have become equally remarkable and useful; instead of which, their pride having subjected them to the
dominion of deceptive spirits, their mediumship faculties have been first perverted, then annihilated, and, in more
than one instance, such mediums have brought upon themselves the most humiliating retribution.” [The Mediums
Book, Chapt. XX]

Pride shows itself in mediums by unequivocal signs.

- blind confidence in the communications obtained by them and infallibility of the spirit whom they emanate;
- they disdain whatever does not come through their own mediumship, and they look at
themselves as having a monopoly of the truth;
- they are dazzled by great names unscrupulously assumed by the spirits who communicate  
through them and their self-love prevents them from seeing they are being deceived;
- they repel all advice from others and keep away those who might open their eyes to the reality of their position;
- even if they should condescend to listen to another, they pay no attention;
- they are offended by contradiction or criticism;
- they may detest those who warn them of their delusion;
- they may withdraw into isolation in which they become the sport of obsessing spirits, who make them accept the
most glaring absurdities as something sublime.

How do we really know a good medium (one in which we may safely confide)?

(This is in regards to mediums who are endowed with the faculty sufficiently developed to admit of free
communication of spirits)

1 - Consider the tenor or tone of the spirit communications obtained (especially of their spirit guides), NOT the
names given by the spirits. Are they of goodness and of a high moral character?
2 - Does the medium  believe his/her mediumship is a gift to be used for goodness?
3 - Does the medium accept the manifestations made through them as a blessing of which they should strive to
render themselves worthy by modesty, kindness, and goodwill?
4 - Is the medium rendered more humble by his interaction with superior spirits?

If the above are answered “yes” then we may conclude that they are basically a good medium. But, one should still
use ones’ reason to analyze all specific spirit communications.
[The Mediums Book, Chapter XX by Allan Kardec. ]