https://www.cheapies.nz/node/55114

It’s pretty easy to set up a trade account (PowerPass card) and the app allows you to scan and self checkout products in store so you can bypass the checkout counters and just walk out with your stuff. 

The Trade Expo has the usual exhibits, presentations and also discounts and free food and drinks. 
You can also log into the trade portal for discounted products but the discounts were small for the couple of things I looked at.