Never tell a client that the agency screw-up was the production manager’s fault, the proofreader’s fault or the CD’s fault. When you do that, you just told the client that you’re not in charge of his account–and you’re losing control. If the effluent hits the fan, take the blame. Shows character and gives the client some confidence that he’s talking to somebody that can get the damn problem fixed.
When things go great, pass the credit on to some deserving person back in the shop. Shows the client that the agency has depth and that you’re at the front of a great team.