My cousin is in the compliance area at the tax office. He tells me that they are more interested in the bigger guys. So if your running a ebay store be very careful. He tells me the tax office feels that it will be pretty easy for them to say your running a business. Having a personal account will be harder for them to call you a business rather than a hobby (although not impossible).
So i agree totally with MandC Perth - if you have an ebay store turning over $50,000+ your going to have a hard time convincing the tax office your not a business. Under tax law the onus is on your to prove your not a business - not the other way around.
If your selling $20,000 worth of stuff on a personal account and your receiving Centrelink benefits look out. Im told this information will just be feed straight to Centrelink the same way they receive all other financial information from the ATO. Being a Financial Planner and having constant dealings with Centrelink they will have a bonanza with this info.