On a large marketplace a single product usually has a single page, and every seller offering that item competes inside it. The arrangement is deliberate, and it explains a great deal about how prices behave there.
A catalogue entry describes a product, not a seller
The record behind the page holds identifiers, images, specifications and accumulated reviews. It exists independently of whoever happens to be holding stock this week.
Sellers attach an offer to that record rather than creating a listing of their own. The page is shared infrastructure and the offer is the only part any individual seller controls.
One result is that reviews build up against the product across years and across sellers, which is why a page can carry a very large number of ratings that no current seller ever earned.
Merging listings keeps search results usable
If every seller published a separate page, a common item would return dozens of near-identical results and the shopper would have to compare them by hand.
Collapsing them into one page moves that comparison inside the marketplace's own ranking logic. The shopper sees a single result with a single default offer already selected.
This is also why duplicate pages are actively merged or suppressed. A second page for the same item splits the review history and weakens both versions in search.
Competition moves to price and delivery
Because the description, photographs and reviews are fixed, a seller cannot differentiate through better presentation. The variables left are price, shipping speed and stock reliability.
That narrows the contest sharply. Sellers of an identical item end up undercutting each other by small amounts, and the price on a competitive page can move several times a day.
Repricing software exists because of this. It watches rival offers and adjusts automatically, which is why a price can drift down through the afternoon without any promotion behind it.
The default offer carries most of the sales
Only one offer is shown by default, and the overwhelming majority of shoppers buy it rather than opening the full list of sellers.
Winning that default position is therefore worth far more than being a few cents cheaper further down the page. The marketplace decides who holds it using a mix of price, fulfilment method and seller performance.
The list of other sellers stays available, but it sits behind a link most people never use. Visibility on these pages is close to winner-take-all.
Shared pages create a quality problem
Since several sellers ship against one listing, the item that arrives may not have come from the seller whose reputation persuaded you.
Stock is also sometimes pooled in warehouses, so units from different sources sit together. Counterfeit and mislabelled goods enter through this route rather than through a fake page.
Checking which seller is actually fulfilling an order, before buying rather than afterwards, is the practical response to a design that hides the seller behind the product.