There never was a bad man that had ability for good service.

Ability and trustworthiness are not separable when it comes to real service. Someone whose judgement bends toward their own advantage will bend it at the worst moment, which is precisely when you needed them, so the talent never arrives where it counts. That is why the brilliant and unreliable so rarely turn out to be a bargain. What you were buying was the outcome, not the capability.

When you are tempted to keep somebody whose work is excellent and conduct is not, count the whole cost, including what others learn from watching. Ask what happens when their interest and yours diverge. Capability you cannot rely on is not capability.