A common idea I have seen expressed in and out of the church is that of the infallibility of the prophets. More specific is the idea that whatever the prophets say can be construed as doctrine if not just authoritative. This belief of course has led to all sorts of traditions and anomalistic doctrines. Things like the Adam-God theory, all indigenous Americans being descended from Lehi, etc.
I came across an interesting scripture last night in 2 Peter 1:20-21.
No prophecy of the scripture is of any private interpretation. For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.
It seems even in the New Testament that prophets need to be moved by the Holy Ghost for their words to be prophetic.
I guess the challenge then is determining when they are moved by the Spirit.