A valid word of knowledge received by a Christian in a Christian setting is coming by the Holy Spirit, in the presence of Jesus Christ and with acknowledgement that scripture sets a precedent for truth. I'll expand on this.

Each person's natural life sphere and zone of experience is this physical realm. In order to have more than this we must either peep over the "wall" into the supernatural realm or, to some extent, leave the natural sphere or zone to enter the supernatural or spiritual.

Many people get a "peep over the wall". This is what makes them aware that there is another dimension to life - a spiritual dimension. This type of experience, however, does not provide a word of knowledge. A word of knowledge is received while beyond the enclosure of the natural realm.

The Christian enters the eternal realm, leaving the confines of the temporal realm, by accepting Jesus as their gateway or doorway. They go through Jesus Christ. (Joh.10:1-9)

They also accept Jesus as their Shepherd both in this realm and in the eternal. The Christian who is accepting this shepherding is then protected in the eternal realm from evil and deceit. They are also led by the Shepherd Jesus to where the spiritual pasture is good. Jesus is their guide to where the spiritual conditions provide nourishing "food". In other words, they are led to where the word of knowledge is wholesome, pure and edifying. (Joh.10:1-16)

The psychic receiving "knowledge" is not operating in this way at all and therefore does not operate with this safety or with this leading to where the "food" is wholesome and pure.