If you’ve ever bought a product from seller you’ve never heard of on Amazon, there could be reason for you to worry: third-party sellers on Amazon are reportedly selling items that have been banned, are unsafe, or have been mislabeled.

According to a Wall Street Journal investigation, the retailer has little oversight over the items being sold on its platform by third-party sellers — so little, in fact, that many items are being sold on the site that would be barred from store shelves.

The Journal was able to identify at least 157 items being sold on Amazon that Amazon itself had previously said it banned. In total it was able to identify 4,152 products that shouldn’t have been for sale on the site. The investigation found that 46% of those products were being shipped directly from Amazon warehouses.

After the Journal pointed out the items in question, Amazon removed or altered the wording on 57% of those listings.

Issues with products range from items that have been banned by federal agencies due to safety concerns to toys and medication that don’t include warnings about health risks. One product for sale on Amazon was a sleeping mat that had been banned by the FDA over concerns that it might suffocate infants.

In response to the story, Amazon published a blog post detailing its process for maintaining product safety and compliance in its online store.

“In 2018 alone, we invested over $400 million to protect our store and our customers and built robust programs to ensure products offered are safe, compliant, and authentic,” the company wrote. “Amazon offers customers hundreds of millions of items, and we have developed, and continuously refine and improve, our tools that prevent suspicious, unsafe, or non-compliant products from being listed in our store.”

Amazon says it vets sellers when they open an account using “proprietary machine learning technology that stops bad actors before they can register or list a single product in our store,” and that all products sold in its store must comply with applicable laws and regulations.

And while that 4,000 number might seem large, Amazon argues that it could be significantly larger.

“In 2018, our teams and technologies proactively blocked more than three billion suspect listings for various forms of abuse, including non-compliance, before they were published to our store,” the blog post says.