Keep good control of client communication. Ensure all important communications are between the project manager and the client project manager, especially for cost, schedule and scope decisions.
The title says it all. Document all communication with your client (and with suppliers and contractors). Even with friendly or familiar clients. Client’s project manager may change, so verbal agreements …
Clarify the terms and conditions with the new project manager. If the client changes during a project (or the client project manager changes), then you as the project manager should …