Looked into the moped/motorcycle rules also. Same BS confusion, same having to speak with two different people at NZTA after the first told me the wrong info. I pity anyone who relies on the verbal advice of no-responsibility voices at these govt institutions.
No more than 50cc and speed-restricted to no more than 50kph then only an initial inspection on first registration needed then no further checks, no warrants of fitness needed (but must stay road worthy), no motorcycle license needed as classed as moped, and significantly lower yearly licensing costs.
So, once the initial rego inspection is done and the classification of moped given, many just de-restrict their scooters so they can get'em up to 80 or more kph. If get pulled over by cops though because travelling more than 50kph, will be breaking three different rules, at least.
Common theme amongst those who want to sell their de-restricted (thus illegal) 'mopeds' is to put their rego on hold and leave it up to the private buyer to rego and thus the new buyer will be the one the cops will ping. So many buyers of second hand scooters haven't a clue about this or just don't care about the misrepresentations the sellers are making about the scooters/mopeds they are selling.
But at least I have learned how to de-restrict a few scooter models now, if I flag the motorcycle license idea. but the whole thing is a dog's breakfast that nobody in the law seems to give a rat's ass about cleaning up.