RedJungle: Attempting to 'take on Trademe' is a path to failure.
I agree with oxnsox, if you can focus on a niche and gain momentum then I could see potential for success. You need a following before you can sell yourself into other/general markets.
Even if you get a niche market level of success (and that itself will be hard) transitioning from niche to mass market is a very difficult step. Youll probably piss off all of your existing customers when you do it.