I have heard it said that a former US President once remarked "People tell you who they are by their actions. When people tell you who they are - believe them."
I believe (and rely) on the concept of grace and forgiveness. This post is not about that. A famous fisherman once asked a famous Carpenter on advice on that subject and if that's what you're looking for then I refer you to that as it is a lot more authoritative than I could ever wish to be.
This post is on trust.
People let us down. They do us wrong. If we're to be honest with ourselves, we find ourselves in those result sets more often than we'd like to admit. We should forgive. Absolutely. BUT, when deciding on future courses of action, it makes sense to evaluate past experiences before deciding on who to partner with.
I can forgive someone for dealing treacherously with me, but does that necessarily mean I have to hire him to be my accountant? I'd argue wisdom calls us to be a lot more objective (and practical) while still trying (and praying) to let mercy reign.