This isn't just a China and chips thing, it's a general supplier thing. My mom ran a small cafe once, and complained that the wholesaler would regularly try to

This isn't just a China and chips thing, it's a general supplier thing. My mom ran a small cafe once, and complained that the wholesaler would regularly try to foist out of date coffee on them. It's something I keep arguing: there's a price associated with policing, keeping, people honest. If there is intense competition, the pressure to cheat is also intense, and what you gain from competition may well be eaten up by the cost of policing. So competition isn't a panacea, it has rapidly diminishing returns. (My mom's wholesaler, though, were pretty much a monopoly, who did this sort of thing just because they could. A different failure case!)