The Advertisers Are the Sellers AgainWide moat

Amazon's fourth customer group is mostly its second one. The advertising business took in $78.0 billion over the twelve months to September 2026¹, and a large share of it is bought by the same third-party sellers who already pay referral and fulfilment fees — purchasing visibility on a shelf they are already renting.

As a business this is close to perfect. The advertising has no inventory cost, sells against demonstrated purchase intent, and can prove its own effectiveness because Amazon observes the resulting sale. It also has a structural property most ad markets lack: the supply of prominent placements is fixed by the shape of a product page, so as more sellers compete for them, prices rise without Amazon doing anything at all.

The tension is that this is a toll on top of a toll, levied on merchants who mostly cannot decline it — an organic listing that nobody sees is not a viable alternative — and it is a recurring theme in seller complaints and regulatory filings. It also gradually degrades the customer experience that made the shelf valuable, since every promoted result is a result the shopper did not search for. Watch advertising as a share of seller economics, and watch whether search results keep filling with sponsored placements. Both are cases where the profitable direction and the durable one diverge.