A large share of what you buy on Amazon is not sold by Amazon. Somewhere approaching a third of units now come from third-party sellers listing alongside Amazon’s own stock, on the same page, in the same buy box, with the difference visible only if you look at the small line naming the seller.
Most coverage treats this as Amazon generously opening its shop to competitors. Look at what flows back and it reads differently.
When a third party sells through the marketplace, Amazon learns the thing that is hardest to learn in retail. Not what people searched for, which any site knows. What actually sold, at what price, in what volume, in which weeks, with what return rate, against which competing listings. That is the information a buyer at a traditional retailer spends a career developing instincts about, and Amazon is receiving it continuously, for free, from people who are paying commission for the privilege of providing it.
What you do with that information is obvious. When a category shows sustained volume at a healthy margin, you stock it yourself. You already know the demand curve, so you take almost no inventory risk, and you can price against a seller whose costs you can estimate closely because they have been trading on your platform for two years.
The seller’s success is the research budget for their own replacement.
I do not say this as an accusation. Every supermarket that has ever launched an own-brand did the same thing with weaker data. The difference is the resolution and the speed, and that the seller has no relationship with the customer to fall back on. A brand that loses a supermarket listing can sell elsewhere. A marketplace seller whose category gets taken has lost the customer entirely, because the customer was never theirs. They were Amazon’s, standing on a page with a different name in small type.
The subscription is the other half and it works on the same principle from the buyer’s side. Pay once a year for delivery and the cost of any individual purchase drops to the price of the item. No postage to weigh up, no basket to fill to reach a threshold, no reason to open a competitor and compare. It converts shopping from a decision into a reflex, and the annual fee makes going anywhere else feel like waste.
Both moves do the same work. One removes the friction that makes a buyer consider alternatives. The other makes independent sellers into an unpaid research function.
Neither requires anything underhanded. That is what makes the position so strong, and what will make it very difficult to argue about later.