Joan of Arc and Evidence of the Divine

Today is the anniversary of the execution of Joan of Arc. She was burned at the stake for being a heretic by the pro-English government of Burgundy for claiming to have Divine inspiration in leading anti-British French troops against them in an effort to reunite France under the Catholic Charles VII. One side believed she was in touch with God and the other side killed her for believing that she was falsely saying so.

What would count as evidence in such a case? If someone came to you in all seriousness and claimed to be able to speak with God, what sort of confirmation would be necessary for such a proposition? What would be needed for reasonable belief?