It depends who's paying. If the product seller pays then it's an advert. If the product buyer pays it's not. The difference in economic incentives is... stark.

It depends who's paying. If the product seller pays then it's an advert. If the product buyer pays it's not. The difference in economic incentives is... stark. Ad supported media has a similarly skewed structure. If I'm paying for media I better like it. If adverts pay for it, the key is lots of people spend lots of time looking at it.