Combine personal visitation with some sort of lab test and then do it again at a different lab. Same burden of whatever as in science. There could be any number of ways god could be shown to be, at the very least, powerful-enough-to-take-note-of in a lab. Take your pick really. It would just have to be something that you couldn't con, so like, I dunno, spontaneously generating a couple gigwatts of electricity ought to do the trick. I don't see how a con artist could pull that off.
Of course, even then, this being hasn't proved it's self to be anything more than a highly advanced alien. It hasn't proved the veracity of the bible or any holy book for that matter, it hasn't proved it created the universe, but at least it would have proved that it's got the potency to back up anything it has to say with deed and that we should probably take notice of this dude.
Of course, even then, this being hasn't proved it's self to be anything more than a highly advanced alien. It hasn't proved the veracity of the bible or any holy book for that matter, it hasn't proved it created the universe, but at least it would have proved that it's got the potency to back up anything it has to say with deed and that we should probably take notice of this dude.