>What makes you think this will be close to 90%? Unless these cards are expensive I don't see that happening.
its obviously just an illustrative guess. but if the penalty of possessing the card is similar to underage possession of alcohol/tobacco, and larger penalties if a store/person is found providing a card to someone underage, i see no reason why it wouldnt have a similar success rate as alcohol/tobacco.
If they have access to the "dark web" they can already do anything that requires age verification there. In the same way you expect that the rule to "not sell UUIDs" wouldn't be respected there, I wouldn't expect other age-verification rules to be respected, no matter the verification method.
its obviously just an illustrative guess. but if the penalty of possessing the card is similar to underage possession of alcohol/tobacco, and larger penalties if a store/person is found providing a card to someone underage, i see no reason why it wouldnt have a similar success rate as alcohol/tobacco.