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.
Well, it's rather harder to sell bottles of beer on the dark web than short text strings.
That is true, it is harder, although AFAIK people do sell all kinds of illegal things there.