So depending where, when and what cultures your players are playing can have an interesting impact on how suspicion trusting can work. So in one of my games one of the players had a suspicion of 13 with a directed trait against Romans due to family history. So every time he goes and deals with Ulfius of Silchester or many of his representatives he is always second guessing their motives toward the Countess Elaine and caused a fair bit of problems for the county due to his mistrust of Romans.
The biggest thing with suspicions is you have to at times as the GM force the issue by telling the suspicious player slightly different information or how the knight might perceive a particular incident, or excuse for an action or inaction by those he is mistrustful of.
Now If the knight is famous for that trait then he should be second guessing everyone for almost every action they do and be planning a response for the worst case scenario due to their renowned paranoia.
Now for the opposite those with high trusting should almost be gullible and not see ulterior motives in what others are doing even if it seems obvious to other player knights. High trusting would be that you expect other people to keep their word.