I use the local auction house "Auction Kings" here in Tauranga and like everything there is a cost but i found them to be helpful and honest and got a lot more for my items than i expected also i didnt have the aggravation of Trademe and buyers turning up on the doorstep or arranging suitable times which can be a long drawn out process. Not saying that every auction house is the same can only speak as i find but to help you i did a look up on google for Nelson and found:
http://www.lipscombeauctioneers.co.nz/
also
J W Auctions with a phone number: 03 5451866
Worth a look i would say and make your own mind up.....good luck