The news: Estée Lauder sued Walmart, accusing it of selling counterfeit versions of La Mer, Tom Ford, Clinique, and other products on its online marketplace. The beauty company also said the retailer did not do enough to ensure that only legitimate and authorized products were offered for sale.

Walmart responded with a terse statement saying that it is “aware of the complaint” and has “zero tolerance for counterfeit products.”

Why it matters: Estée Lauder’s suit reflects the tensions inherent in operating online marketplaces—particularly for retailers like Walmart that are trying to grow as quickly as they can. Lower barriers to entry for sellers can enable marketplaces to quickly expand their product selection and increase their appeal to shoppers, but being too hands-off can open the door for counterfeiters and other unauthorized actors to break through.

However, Walmart stands accused of not merely making it possible for counterfeit products to be sold, but also of actively facilitating and profiting from their sale. Estée Lauder’s complaint contends that the products were advertised to shoppers on Walmart’s marketplace, and that the retailer used Estée Lauder trademarks in search engine optimization tools to increase traffic to the listings.

Implications for retailers: Estée Lauder’s suit is unlikely to materially derail Walmart’s ecommerce ambitions: We expect the retailer’s third-party marketplace sales to grow 14.5% this year, and account for nearly 11% of its online sales. But with growth slowing, Walmart can ill afford to antagonize brands, especially as it looks to court wealthier shoppers with more upscale products.

The accusations show the need for retailers to have stricter vetting in place for sellers and products. Marketplaces that lack such measures risk alienating brands like Estée Lauder that could otherwise add to their cachet, as well as shoppers wary of knockoffs.