On the second evening of Prime Day, Amazon’s annual sales bonanza, Anne Marie Bressler received an email from Amazon that had nothing to do with the latest deals. The message, sent from an automated email address Tuesday, informed her that the Align nutritional supplements she ordered two weeks earlier were probably counterfeit. “If you still have this product, we recommend that you stop using it immediately and dispose of the item,” the email reads, adding that she would be receiving a full refund. It’s not clear how many other customers may have purchased the fake supplements. Amazon confirmed that it sent out the email but declined to specify the number of customers impacted.

For years, Amazon has battled third-party sellers who list knockoffs of everything from iPhone charging cables to soccer jerseys on its site. Nutritional supplements are another popular target for fakes, as it’s a largely unregulated industry. The US Food and Drug Administration has been criticized—including by former staff—for declining to test dietary supplements for safety and effectiveness the same way it does pharmaceuticals. In this instance, the problems came together: An Amazon merchant sold dupes of genuine probiotics made by Align, a Procter & Gamble brand.

“We are aware that some counterfeit Align product was sold on Amazon via third parties,” Mollie Wheeler, a spokes­person for Procter & Gamble, said in an email. “Amazon has confirmed they have stopped third party sales of the Align products in question and Amazon is only selling Align product received directly from P&G manufacturing facilities.”

Louise Matsakis covers Amazon, internet law, and online culture for WIRED.

In a statement, an Amazon spokes­person highlighted several initiatives the company has devised to detect counterfeiters, like Brand Registry and Project Zero. Brands typically need to elect to participate in these programs, and the spokesperson declined to clarify whether Procter & Gamble or Align were already enrolled.

“We investigate every claim of potential counterfeit thoroughly, and often in partnership with brands, and in the rare instance where a bad actor gets through, we take swift action, including removing the item for sale, permanently banning bad actors, pursuing legal action, and working with law enforcement when appropriate,” the statement reads. “We have taken these actions against the bad actors in question and proactively notified and refunded customers.” Neither Amazon nor Procter & Gamble would say who first detected the fake pills.

Amazon also didn’t respond to a question about whether it would test the counterfeit probiotics, leaving Bressler and other customers to wonder if they may have ingested something dangerous. The FDA has found that supplements sometimes contain prescription pharmaceuticals like steroids or antidepressants, which can be harmful if a person takes them without being aware of it. CVS recently announced plans to independently test every nutritional supplement it carries in its stores. That Amazon isn’t doing the same might sound careless, but the reality is that the company has already taken far more action than it’s obligated to under the law.

Even if the counterfeit Align pills Amazon sold turned out to be harmful, Bressler and other buyers would likely have little legal recourse against the company. When consumers have tried to sue online marketplaces like Amazon and eBay for selling dangerous goods in the past, courts have ruled they aren’t responsible for products offered by third-party vendors—they serve merely as intermediaries between consumers and sellers.

In many of these cases, the companies have defended themselves using Section 230 of the Communications Decency Act. Passed in 1996, it shields them from nearly all liability for what sellers or users post on their sites. In one 2014 case, for example, a judge found that because of Section 230, eBay isn’t liable even when it sells items that have been recalled. “Marketplaces aren’t responsible for passing along recalls, even if they know the recalls have been issued, and even if they would have the capacity to share them,” says Eric Goldman, a professor at Santa Clara University School of Law who has written extensively about intermediary liability. (Items that have been recalled, however, are prohibited under eBay’s Terms of Service.)