Health professionals are concerned about the risk of skin cancer caused by sunbeds purchased of TradeMe.
Regulations have been tightened in recent years around commercial sunbeds, but research has revealed private sunbeds don't have regulations and may cause harm to users.
"It's a concern that ex-commercial sunbeds can be sold on the second-hand market, because consumers will continue to be exposed to excessive levels of ultraviolet radiation (UVR), which is the primary potentially preventable cause of skin cancer," researcher Bronwen McNoe says.
The research counted how many sunbeds and sunlamps were available for sale on TradeMe and how many were ex-commercial.
From November 2015 to September 2017, there were 266 sunbeds or sunlamps for sale, a quarter of which had previously been used commercially.
More than half were sold for less than $1500 and at an average of $186, making them cheap for consumers.
Ms McNoe is concerned about the lack of information provided with second-hand devices.
"This is a completely unregulated environment, with unjustified health claims being regularly made and no information provided on reducing the risk of product use," she said.