Quality control

Dear Sir, could you please explain in simple words the following extract (it is under the sub topic of "Accepting nomination to auditing engagement"): "You should know that communication with the existing auditor is not just a matter of professional courtesy. Its main purpose is to enable the professional accountant to ensure that there has been no action by the client which would on ethical grounds to preclude the professional accountant from accepting the appointment" The formulation of the idea here seems complicated and I can't understand the idea.