I was a young engineer visiting Massachusetts for a chip-bringup.
A college buddy had ditched engineering and was at Harvard law.
I stopped by his dorm and played a round of Diplomacy with them. I'm a terribly trusting person, and my "honesty is the best policy" style of gameplay did not leave my nation in the best of positions.
I heard one of the world's top diplomacy players is actually plays honorably like 95% of the time. He makes deals with almost everyone early on and generally to their benefit more than his own since building repoire and trust with folks allows you a greater deal of leverage over more of the board. But that's at the highest levels of play.
I played a month long play by e-mail game once with some friends in college. About half of them no longer talk with me because of that game hehue.