Which? said it found more than a dozen listings of illegal car seats on websites such as eBay, Little Dreams, ManoMano, Shein and Wish.
One listing for a child’s car seat on eBay warned against using it in cars despite the product being described as suitable.
The description in the listing read: “It is best not to use it on high-speed cars.
“We recommend that it be used in non-motorized products such as electric vehicles, two-wheelers… Because it is not a child safety seat that complies with traffic.”
In response, eBay said consumer safety “is a top priority”.
“We swiftly removed these listings and notified buyers, and we continue to strengthen our preventative measures,” a spokesperson said.
Which? said stricter rules were needed to “impose a clear and robust duty on online marketplaces to prevent the sale of unsafe products” and called for “strong penalties and rigorous enforcement”.
Sue Davies, Which? head of consumer protection policy, said: “It is appalling that these deadly car seats are reappearing on online marketplaces more than a decade after Which? first exposed them, but it is not surprising.”
She said children’s lives “will be at risk” until online retailers were forced to comply with product safety regulations.