I think the best reason is to just accept that God cannot be proven, and name faith as the reason for believing. While it's not logical, I would never deny that a person has such faith. For me, it's only when believer tries to prove god exists, that logical arguments come into play. If a person believes it because he believes it, it adds no credibility to the existence of god. It's not even an argument, but I accept that the person is sincere, although not very good at reasoning.