Belief

Reading The Miracle Detective, I wondered , if someone appeared before you and said he/she was God(or related to God), what would it take for you to be convinced?
Lets assume that any act (e.g. turning night into day, blossoming flowers in winter, levitation, teleportation) etc are performed by said entity at a snap of a finger. Would you believe?
And then I wonder suppose there is a devout Hare Rama Hare Krishna type who believes say Krishna is the only true god and also believes lets say the Bhagwad Gita as the literal word of Krishna. If the entity appears to him, says Yes I am Krishna , But the Bhagwad Gita are not my words , my teachings are actually closer to whatever Buddha(Or Christ or Mohammed) taught. Would the devout person believe? or would he think he is being hoodwinked by an Asur?
What if the entity says, yes the Bhagwad Gita are actually my(God's) words but Im not krishna Im actually Buddha(Or Christ or Mohammed) would the devout person believe? or would he think he is being hoodwinked?
And what if the entity says sorry , you chose the wrong gods neither the philosophy nor the god you believe in are correct. Would the devout person believe?
Note that any miraculous activity can be performed by said entity without any problem.
In most cases I think we'd only believe if the entity said exactly what we believed in before we encountered the entity.
I guess Mark Millar touched upon this topic in Chosen , before he chose the ending for shock value (oh what a book it would have been if Millar had chosen(pun) a different ending).