Large retailers do this with store brands (Walmart), but it's generally more opaque to the consumer.

It's really quite clever, you sell third-party products, but also control all transaction data — so you see which products are successful, somewhat well reviewed, and profitable... then you just steal the business.

It's kind of how Apple/Google adopt features. Watch which utility apps are popular, then just build the features into the OS.

If you're relying on a third-party to sell your product in a marketplace, you can't get too comfortable.