It's not a matter of being trusting or not lantz.
If you include the characters' weaknesses in their sheets, and someone tries to take advantage of them in character despite having had no way to gain such knowledge, it will be obviously recognizable as metagaming. And I doubt anyone will let metagaming with significant effect on the RP or done in a blatant way to pass.
Have you ever heard how kindness is "paying it forward"? Trust is also kinda like that, lantz.