I guess if I was your customer, not knowing what product or part you make, I'd be concerned about your designation of the product and how your process prevents its use or shipment. For example, we process steel. If something is found to be non-conforming, it is placed on "hold" electronically, and even if another process WANTED to process it further or even ship it, that would be impossible because the act of putting it on "hold" in the system constrains it - prevents it from being processed through at a machine, or prevents it from being billed out. So it CAN'T go anywhere. Same is true if we then decide that hold material is no good and should be returned to stock for another use or scrapped - the act of RTS'ing it or scrapping it means it literally CAN'T be processed or shipped. I think that's probably the kind of thing your customer is looking for.
I get nervous when I see systems - and yes, I realize theres a LOT of them out there, not everyone is as electronic as some - where material that is non-conforming is just isolated in a special area or someone hangs a hold tag on it. There's really nothing in many of those types of systems to stop someone from walking over to that part or material, picking it up, and making something out of it or shipping it. Your customer is probably looking for a step of somekind you take to make SURE if it's on hold it can't be used or shipped.