Phia, an advertising startup co-founded by Phoebe Gates, daughter of billionaire Microsoft Corp. co-founder Bill Gates, bills itself as a “personal shopping assistant” that helps users find the lowest prices on a broad range of clothes and fashion accessories.

Download the Phia tool onto a web browser, use it while shopping and — voila — the so-called extension can quickly find discount codes for products. Businesses like these, known in industry parlance as affiliate marketing programs, typically collect a commission from retailers that make the resulting sale.

But according to Ben Edelman, an independent researcher and consultant who studies affiliate marketing, as well as Capital One Shopping, which makes a competing browser extension, Phia is claiming credit for online sales it didn’t actually drive, in violation of many digital platforms’ policies.