I gotta admit, using the preconceived concept of "good and evil", and then sifting it through the D&D kind of good and evil, is a good twist.
Even if the priest guy was an obvious bad guy, it's also easy to rely on your abilities. If what you rely on says "nope, he's okay", you're not going to believe that anything's wrong.
That being said, if I thought about this story as a D&D game, and not a silly RP adlib story, then the priest would indeed be suspicious, no matter what. Zealots are trouble, no matter how you slice it, unless you know exactly what triggers them and what doesn't.