Items aren't inspected deeply when they arrive. Fakes can get in.
Items that are misplaced and later found are presumed to be good- no quality checks opening the package. If the barcode scans, the system just adds it.
The picker, sorter, packer all do a quick quality check to see if the box is broken. They sure aren't opening it to see what's inside.
All that's left is the weight check as the package leaves the building. The putty the scammers use weighs exactly the right amount.
The only time the item might be checked for being correct is when it's returned. And they do that because a lot of scammers buy the real item and then send back a box full of putty.
My guess? Someone didn't do a complete check on a previous return- hey, associates have to make rate or they'll be fired, corners get cut. The fake got restowed, resold, and then the second time it was returned someone did a real check.