If "God" was standing right in front of you, right now, in all it's inexplicable and blazing glory, you would still have no way of determining that it was actually God. As opposed to some sort of self-generated mental delusion, or some clever magician's illusion, or some advanced alien species masquerading is "God" for your, their, or some other purpose. There simply is no degree to which you could experience God and be certain that what you're experiencing IS God, because as a human, you are simply no equipped to verify the conditions and characteristics that we attribute to our concept of "God". In this respect, I can speak for and to the limitations of all humans.