While I agree with your sentiment, Andy, this was apparently a customer auditor so I think the push back should be a little more gentle.
I would certainly push back on the NC and express that this is not a special process and you verify the output of the equipment though appropriate sampling and/or monitoring.
Have you done any IQ/OQ on any of your other equipment? Is the customer that wrote this up in the regulated world (drug, device, auto, aero, etc)?