A teaching of Jesus' during The Sermon on the Mount
Jesus tells us to be wary of false prophets. He tells us that a thorn bush will not bear grapes, nor will a briar bear figs. These false prophets are sheep on the outside, but wolves on the inside. The good tree will bear good fruit - the bad tree will be cut down and burnt...
The message to me is that we should judge people on what they do - not on a reputation or rumour. It's easy to listen to a rumour - person A is a fantastic coder but difficult to get along with.
I have a slight problem with judging others solely by their actions - I spent a long time helping a girl who worked with me, only to find out that she hated me and boasted about using me to her friends. While I found out eventually, I had tried to remain blind to reputation - and wound up bitter over it (for a short while). I suppose my advice would be to keep your eyes and ears open; the wolf in sheep's clothing can be hard to spot.