Thousands of suspicious reviews have been discovered on top-rated products on Amazon UK, propelling devices from relatively unknown manufacturers to the top of the search results. The findings come from British consumer goods review site Which?, which investigated multiple product categories, including headphones, dash cams, fitness trackers, and smartwatches.

In the headphones category, for example, the investigation found that the first page of the top-rated list was dominated by relatively unknown brands. These products had thousands of positive unverified reviews, often posted in quick succession, and The Guardian notes that they occasionally included text that referred to entirely separate products like soap dispensers. In the headphones category, 71 percent had perfect five-star ratings.

“We suspend, ban and take legal action on those who violate our policies.”

One pair of headphones from a brand called Celebrat received over 400 five-star reviews on the same day. The brand could not be reached for comment by Which?, BBC News, or The Guardian, and it does not have any public-facing website to allow it to be contacted.

In a statement, Amazon said that it invests “significant resources to protect the integrity of reviews” and that it will “suspend, ban and take legal action on those who violate our policies.” It added that it uses both automated machine learning technology and teams of investigators to detect, block, and remove inauthentic reviews.

The report suggests that Amazon is still struggling to contain its fake reviews problem. Recently, the Federal Trade Commission successfully brought the first case against a weight-loss supplements company in the US that was using fake Amazon ads. Amazon issues harsh punishments for those it suspects are paying for or posting fake product reviews, but this system has been open to abuse in the past by sellers who have paid for fake reviews to be posted on their competitor’s products and then report them to get them banned from the service.