Paid for auction won, seller wants more money for item.

Hello kirby. This is one of those "It depends" questions. A seller is covered if they have made a genuine mistake. I once sent out a Fixed Price Offer for $50 (meant to be $500.) In these cases it is quite OK for a seller to cancel it as a genuine mistake. 

However if it's a $1 reserve auction or similar, and the seller just wasn't happy with what they got then in theory you could force the issue. At the end of the day though you can't get blood from a stone. While you do have a legal contract there to buy it at the price you won it for, if the seller digs his toes in you can't really get blood from a stone. 

If you want Trade Me to intervene on your behalf the best way forward there would be to open a Dispute for this trade. You can do this from your won page. 

Hello kirby. See attached 

I hope you got your money back that you already paid.