It asked Trade Me for a list of sellers offering high-risk items such as electric blankets, power chargers and decorative lights in commercial volumes in the past 12 months, and 1,400 Trade Me members were picked out.
"We reached out to each of these memberships and advised them that their details had been released to Energy Safety for the purposes of an electrical safety audit, and reminding them of their obligations under the Act," Duffy said.
Sellers could download the form from Energy Safety but would also need a test report from the manufacturer, or to have a product or device tested by a certified electrician.
Electrician Phil Rumble said most would do it for $25 or $30. He said he had started to refuse to install electrical equipment that had been bought on Trade Me if it was not up to standard. "I would be liable for it and it's just dangerous."
Duffy said Trade Me was not aware of any fines as a result of Energy Safety's recent activity. "But historically a number of our members have been fined for non-compliance. This is serious stuff for us - unsafe electrical items can harm people and cause fires. For repeat or serious offending non-compliance, Trade Me will terminate memberships to protect buyers."
In 2010, 25,000 Trade Me members sold more than 350,000 external power supplies, such as chargers for mobile phones and power supplies for laptops. A ministry spokeswoman said a sample of those who had sold more than 100 units revealed that 90 per cent of them had been sold illegally and 75 per cent had no way of establishing whether or not the product they sold was safe.
"This represented a huge risk to New Zealand consumers as these are the primary means of connecting very common devices to mains supply. Energy Safety issued 36 infringement notices then repeated the exercise annually."
Last year, 10 per cent could not establish a basis for safety, and Energy Safety issued two infringement notices. Trade Me removed 6,000 listings made by 4,000 traders through their own policing and community watch.
One Trade Me seller, David, said he would stop selling all 230V supply items.
"There's no reasonable way for me to absorb the extra costs of being certified."
Mark Devlin, who also received a warning, said 20 seemed an arbitrary number. "You don't get a warning with each listing that you might be expected to supply a certificate in future."