If it's someone I know well, I try to find out why. Usually, the root of a lie is fear. Fear of loss, fear of being hurt, et al. Do I trust em again? Hmmm... depends on the level of the lie. We all do in some form or another, either a lie of ommission, a white lie at work, or amongs people we know, we lie about excuses... and anyone who says they don't lie ... just did.
It's a matter of degrees