I don’t think that Charming believed what Rumpel said at all. I think Snow did. And Charming was just being logical about it. If you believe part of what Rumpel said then you need to believe all of it. And believing someone is telling the truth is not the same thing as trusting them, in my opinion. Pretty much Charming’s entire world has been turned upside down by Rumpel and not in a good way and when it comes down to it i am pretty sure the same is going to be true for Snow because of Cora and Regina and that is not even mentioning the whole incident with the dark curse for which Rumpel is very much responsible for.