A friend of a friend tells me that nowadays it is often an inside job. I.e. someone like the owner of the DH Gate platform who is probably based in that region of Asia will contact factory workers and offer a cut to whoever's job it is to reject an item for being 'defective'. As long as numbers are kept believable, the big companies won't bat an eyelid if say 200 units out of a production run of 10k is marked down as a sunk cost.
All defective items are meant to be destroyed, but they magically find their way into a garage somewhere instead of a furnace. And from there, they are sold for circa £10-15 profit to the likes of us.
The item won't have official labels on it because they aren't affixed until the item is confirmed as non defective. This preserves the label's reputation, protects against shady business (lol), and ensures that most if not all defective items moving forward will be blamed on the shop due to transit, storage or display/handling.
Which is why so many of these fake kits are indistinguishable from the real thing, with the exception of the inside labels.
Anyway, that's your weekly bulletin from CK's Citizens Crime Advice Bureau.