Paul Atreides is never characterized as a fraud in the universe he exists in. That is entirely a notion that comes from the discourse around DUNE but not the text itself.
There are ample chances across the novels for this to occur by characters with a motive to do so. Yet they never do. Infact their terror isn't that Paul Atreides is a fraud. It ts that he's too real and exactly what he is presented as being. A real Messiah with genuine extra temporal perception.
Which actually brings us to the fact prophecy is a necessary mechanical function of the Dune Universe that literally holds it altogether and makes it function. This is not sleight of hand or manipulation but actually walking the pathways of possible outcomes and making choices with that information.
You cannot on onehand agree Paul Atreides has what are by any definition Messiah level abilities and then turnaround and call him a fraud. But we really don't need to entertain that argument because the text itself never does it.
Moreover. God Emperor of DUNE just in case you had any doubts restates. Yes Paul Atreides was The Messiah. And it should be noted not a messiah among many but capital M The Messiah.