Gotta hand it to these guys - I made the mistake of booking a flight thinking the quote was in New Zealand Dollars. Shortly after I confirmed the reservation and paid I realised my mistake and that it was a lot more expensive than I thought (USD), and got in touch with them via their live online chat. Talked to real live customer service person in New Zealand - friendly and extremely prompt (late on a Saturday evening) and Gary cancelled the flight for me with minimal fuss of proving who I was (this can only be done for free if you contact them within 4 hours of making the booking).
Customer services Gary said it would take 7-14 days for the refund to come through, but in fact the pending transaction just disappeared from my account, so I essentially got the money back immediately. Very happy with their service and ended up booking one of my other flights with them.