Location set to NZ but products not in NZ?

No Sarah, unfortunately the sellers membership location is not necessarily the location of the items for sale and the location filter for buying is set to use the sellers membership address rather than the product location. We have been asking Trademe for some years to make the buying location filters use the product location rather than the membership location, but no change, as yet. All you can do is set the location when searching to NZ, then add a - "china" to your search string and also look at the shipping time estimates although not all sellers use those. Worse than what you mention are the sellers that have a membership that says location New Zealand, but they are actually in Malaysia or elsewhere and make no mention of where the goods are. At least if it says China in the text, you can search filter to not see them although this is a clumsy difficult hit and miss approach that will exclude some legitimate items.

If sellers were made to set product location then location search filters would work as intended. 

Okay thank you for answering and for your help :-) that makes sense.