But spotting the dishonest from the honest is a crucial theme for crime stories and should play a part in most tales, regardless of genre. This is because there is bound to be at least one dishonest character (I can't think of an honest villain off the top of my head!) and their actions, sometimes inactions, are bound to have consequences effecting other characters/the plot. Also stories are nothing without conflict and the best conflict for story purposes, I think, is between good and evil.
So how do your "good" characters spot the bad ones? Are the bad ones obvious or is their villainy revealed slice by slice (literally perhaps if writing horror!)? Good characters shouldn't be nauseatingly good, they've got to win your readers round to their side. Bad characters should have some redeeming features given very few of us are unremittingly evil and fiction should reflect that. But all your characters should seem real to your audience. There should be something about your characters that others can identify with. And that is how you tell the real from the fake!