^ GST is a flat 15% tax except as Brooko rightly says there's a small allowance before it gets applied.
I wasn't aware of 5% duty on amps!
Kiwis buy a lot from overseas, meaning NZ customs is overwhelmed from time to time. I got the benefit of this once or twice, some very expensive gear coming straight through.
Personally I'm not annoyed by GST. Even with this it's almost always cheaper than buying the same product from a NZ retailer (who has other costs they have to factor in, especially on items with a small market).
What does annoy me is the lengthy process sometimes. When I bought my LCD2 direct from Audez'e 2-3 years ago, I had to go through the rigmarole of applying for an import licence for this private purchase
Took weeks, and I still don't understand why, as other more costly items only attracted the usual 15% plus IETF plus a few days delay. Or - as noted above - I got lucky and they were sent straight to me.