Relationship audits are great tools for getting to know how your clients really feel about their work with you.
This is a one on one interview process with your clients. You choose clients that may be troubled or in danger of leaving. You may also want to interview star clients in order to boost your relationship with them.
Together with you, I would design custom interview questions specifically created for that client. I would interview the client and report back to you any concerns the client may have or any person the client may be having some difficulty with. I would coach the person/team working with that client to build a more effective relationship and strategy.
This enables you to fix any relationship issues and build a more solid base with that client. Often there may be hidden issues, the client is reluctant to bring up. It is my experience that this not only helps you gain important information but is a great PR tool. Clients love to be asked.