Personal information requested by the ATO includes names, addresses, telephone numbers, email addresses, user IDs, dates of birth, dates of registration on eBay and monthly sales data. Some eBay users are already panicking in posts on the site's discussion boards, saying they were unaware they could be considered tax cheats.

In Australia eBay has over five million unique users and research by Nielsen in 2006 found there were 52,000 Australians who derived either a primary or secondary income selling on eBay. That number is likely to have increased significantly since then. An ATO spokeswoman said: "This is one of the tools that we use to check that people are declaring their income properly and we do it across a whole lot of industries, not just online trading." Adam Micmacher, partner with the Lowensteins Arts Management accountancy firm in Bondi Junction, said the move was a sign the ATO was "expanding its reach to internet-based trading platforms like eBay", noting that it would appear that the ATO would now scrutinise transactions at e-commerce sites like eBay just as intensely as a shop on the street.

But the ATO's initial request suggested those earning less than $50,000 annually from the site would escape relatively unscathed this time around. "However, if for example this initial review bears fruit, they might come back again and now ask for people who sold, for example, $30,000," he said.

The ATO said the high income cut-off did not mean the ATO had no chance of catching eBay sellers who did not declare all of their income, "because we also data match reported income with bank records". Mr Micmacher said the ATO may also seek out people who have not paid capital gains tax on one-off sales of high value items such as paintings. "Somebody may have, for example, just sold two private paintings that they've owned for 20 years over eBay, but that doesn't necessarily mean it's going to be income," he said.

"In that circumstance it might throw up that the person may have been subject to report a capital gain from having sold those items." eBay user Maureen Chuck said she never sold enough to warrant a look from the ATO but she regularly saw "some very silly people who are selling high volumes who because they call themselves 'stay at home mums' think they [are] tax exempt".

Mr Micmacher agreed that it may be difficult for some part-time sellers selling second-hand goods to determine whether they are running a taxable business or simply selling knick-knacks as a hobby. "You have to look at the traditional aspects of business. Have you got a business plan, what is the size and scale of the operation, how many transactions do you do a year, are you really holding yourself out to be in business, have you registered with the Government to be recorded as having an Australian Business Number, how do you run your business or are you doing this truly has a hobby?" he said. eBay Australia spokesman Daniel Feiler said the auction site was legally obliged to provide the ATO with the requested personal information of its members.

"We believe that the majority of eBay sellers do the right thing but I think the simple point is that if you're selling on eBay to a point where you are reaching the threshold where you're required to pay tax and you're not doing it, then you're really stupid," he said.