I didn't see any skepticism from Dr. Oz or the audience. He was his usual overly-earnest self, intensely focusing his attention on his guest in an attempt to create the illusion that what they are saying is actually interesting. To the extent the audience members shown had any reaction at all, they looked like they were mildly bored to me.
Dr. Oz pointing out that miso soup doesn't usually have fish in it didn't seem like an expression of doubt about Bethenny's story in my opinion. I think he was just playing at being a journalist, emphasizing the unexpected twist in the series of events that lead to all the drama. He doubtlessly knew all the details of her story before she ever walked out on stage ... I'm sure he didn't invite her to appear so he could expose her as a fish allergy fraudster, lol. That kind of thing is Dr. Phil's schtick, not Dr. Oz's.
But ... but ... Luann is such a delicate dew drop, while Bethenny is ... Bethenny. You're not suggesting the same rules be applied to BOTH of them, are you? That's insanity!