...although it is possible to outwardly assure someone of something and yet be lying.

Surely, Alex, you're not suggesting that someone may smile and smile and be a villain? Nah, never happen!

Theresa, I don't think there is a simple verb which fits your bill. The concept of non-trickery must be so commonplace that no one ever needed such a word!

Except, of course, the Ferengi, as ?dxb suggested above ...

- Pfranz