1. Buy a “personal, domestic, or household” item for your personal (non-business) use
2. For a fixed price (i.e. on a “Buy Now”)
3. From a seller who is “in trade” (not a one-off seller, like a family selling their bike, but a regular dealer / shop / importer / etc)

[all of those things]
then the Consumer Guarantees Act WILL usually apply. That means you have a number of rights against the seller (which cannot be contracted out of). See sections 5 to 13 of the Act in particular: http://www.legislation.govt.nz/act/public/1993/0091/latest/DLM311053.html