>Big tech and battery makers don't buy ore straight out of the mine; as you say, they buy from suppliers, who are typically always willing to certify they don't use child labor.
Again that points towards not just culpability (knowledge they are facilitating child exploitation and labor), but willing to go so far as to have their suppliers provide certifications they know are "often" fake.
>The question is how you, as a purchaser for Google or whatever, can actually catch the lie.
Plenty of other similar mining industries that exploited child labor have managed to put systems in place to minimize and weed out such practices. If De Beers diamond company can improve...certainly the big data tech companies can do better than requiring certs they know are often fake.