Hi.  It will not be Trade Me directly saying your Rural. It will be up to the Courier Company Delivery Maps.   Aramex has different Rural areas to NZ Post. So while you may not be Rural  with NZ Post you might be classed as Rural with Aramex or vis versa.

Ask then for a Non Rural Address to send it to.  Or I just cancel the Trade.

I have encountered this.  I have on my auctions that I go by the NZ Post maps as to whether people are rural or not. I give the buyer the option of sending the item to a Non Rural location. If buyer still insists they are not rural and refuse to pay extra postage I just cancel the trade.

You agree to the shipping costs when you buy.  Unless you ask the seller questions about shipping first.