Those rules might apply to the sender… but the customer who places the order doesn’t get off so lightly. They can go to jail for five years for importing a drugs without a license.
That’s not even really a vape thing. Nicotine is a drug. Importing cigarettes is also illegal with the exception of travellers in person can bring a few packets with them.
It wouldn’t be hard to catch people - international shipping requires labels declaring the contents. And if the vape seller is lying on those declarations then they’re breaking NZ laws.