Amazon says it "regrets" that suspect child car seats have once again been found on sale on its UK store, and says it has removed them.
The products were discovered by BBC Panorama as part of a wider-ranging programme.
The US firm has repeatedly faced complaints about listing such seats.
A case dating back to 2013 led to a trading standards investigation that confirmed one example would tear apart if involved in a 30mph (48km/h) crash.
More recently, Which? magazine found examples on Amazon of fabric-based seats that lacked the required safety labelling in 2019. Other outlets, including eBay, were also found to be selling the items at the time.
No safety labels
Four obscure brands were involved in the latest case.
One listing described the product as being an "Infant Safe Seat" capable of preventing injury to a baby if a car urgently braked. It was on sale for just £3.99.
Panorama attempted to contact the brands involved. It received a reply from only one of them, which said it was not the manufacturer.
The programme purchased three of the suspect seats. They appeared similar in design to some of those involved in the 2013 case and lacked safety labels.
The documentary-maker alerted Surrey Trading Standards at the start of January. Officers have begun a fresh investigation but have yet to publish their findings.
Amazon's UK chief said the company took proactive steps to ensure the products it sold were safe.
"Automated algorithms [survey] over five billion product pages every day and we monitors tens of millions of customer reviews," Doug Gurr said.
In a follow-up statement, the firm added: "Safety is extremely important to us and we regret that these products were available from third-party sellers using our stores.
"After a thorough investigation, we identified the issue and are removing these products, and we're also contacting each customer who purchased one of these products to explain the situation and issue a refund.
"We will continue to leverage and improve our tools and technology to ensure only safe and compliant car seats are available worldwide."
At present, the operators of online markets, including Amazon Marketplace, are exempt from liability if they are not aware of illegal content being sold on their platform.
But Which? has campaigned for this to change as part of the forthcoming Online Harms Bill.
"The voluntary nature of current checks by marketplaces fails to recognise their role as the primary interface for consumers with the technical, as well as commercial, ability to hold their suppliers to account for consumer safety," it blogged in November.
"Clearer government guidance is needed while this legislation is being drafted."
Amazon has sent emails to consumers who purchased the removed seats.
They said: "The product you received from a third-party seller may not be compliant with applicable child restraint standards.
"If you still have this product, please stop using it immediately, cut the straps to ensure it cannot be used, and dispose of the item."
Amazon: What They Know About Us will be broadcast on BBC One at 20:30GMT