John
I think I would have been a little more proactive in sorting it out, partly to get to the bottom of it for myself and to show concern for the customer, even though they may be partly responsible for it.
Get round there and see where the problem is and perhaps spray a deoderiser on. I would reclean if custy would let me, but I'm very confident my kit and technique is not the cause of problem. If you have had this three times I be concerned it's your vac motors or your wanding.
Mike