In 'Othello', how does Shakespeare suggest that Iago has built a reputation for being trustworthy?

Throughout the play, characters appear to trust Iago. But why might this be the case when, we, as an audience, know he his far from a trustworthy character? There are perhaps three key reasons why characters trust Iago to begin with:

1. Iago maintains the façade that he is “honest” by seeming to be a plain speaker, i.e. someone who says what he feels and thinks. We have evidence for this in the open language which Iago uses in his first speech. Here, he tells Roderigo that he follows Othello “to serve my turn upon him”. Roderigo is likely to trust a man who appears to be so open about his motives and desires.

2. Iago is in a position of authority and therefore trust. He is a soldier and serves a valiant general. We are likely to have preconceptions of people in these kinds of positions, and to an extent assume them to be trustworthy. Perhaps even if Roderigo were a “plain speaker” we would be less likely to be manipulated by him, as he is not in a particularly honourable position.

3. He gets others to do his 'dirty work', and distances himself from his evil. He makes his “fool” his “purse” and in the process constructs a tool for manipulation which keeps him self at a distance from his evil.