I agree that the characters who raise our suspicion all show duplicity in their language and are poor listeners. I noticed Gen. Tilney often soliciting Eleanor's opinion and then giving her no opportunity to share it (e.g., Ch. 22, as they're discussing Woodston:

“Is it a pretty place?” asked Catherine.

“What say you, Eleanor? Speak your opinion, for ladies can best tell the taste of ladies in regard to places as well as men. I think it would be acknowledged by the most impartial eye to have many recommendations."

And then he goes to to expound on what he thinks, describe its features, and discuss their finances.

JA also uses duplicitous language to describe these characters at times, particularly Isabella. One of my favorite lines of this whole book is describing Isabella as having "smiles of exquisite misery and the laughing eye of utter despondency" (Ch. 9). This kind of description, paired with her frequent duplicitous behavior (e.g., railing against the two young men and then chasing after them, or declaring that she wants to sit somewhere out of the way and then taking the seat that's smack dab in the middle of things, or insisting that she won't dance and then doing so, and on and on and on...) at first strikes me as just the words and actions of a fickle, flirtatious girl. It will be interesting to see, as the story continues to unfold, whether it stops at that or reveals something worse (though her reactions to James at the end of Ch. 20 don't bode well).