Selling personal items on Trade Me

If you sell a personal item on Trade-me there are no tax implications for you. But if you have got into the habit of buying items with the intent of selling them for a profit, then you must declare the income and the costs associated with those deals and pay tax on the gain (profit).  Example: If you buy an item for $40 and on-sell it for $100, then you must pay tax on the $60.  If you also paid for the postage (say $10), then you can deduct that from the $60.  The simple  arithmetic looks like this: $100-$40-$10=$50
The $50 you must share with the tax man in your annual tax return. Don’t get caught out as the IRD will eventually catch you and then you will have find tax plus the penalties for not declaring it earlier.
https://www.ird.govt.nz/ecommerce-tax/onlinetrading.html