How do I know the attorney's fee is fair? 

The fee charged by a bankruptcy attorney for representing you in a Chapter 13 case must be reviewed and approved by the Bankruptcy Court.  The Bankruptcy Judge will only approve a fee if they find it to be reasonable.  In most cases, the Chapter 13 attorney fees are paid through your Chapter 13 plan payments.  In many places, like the Northern District of California, the Bankruptcy Courts have set fee guidelines which attorneys must comply with in Chapter 13 cases.