The buy box, and why it moves
How marketplace buy-box ownership works, why it flips, and what a seller change signals before the price move that follows.
On a marketplace, many sellers can offer the same product, and one of them wins the default position that most purchases flow through. Ownership is recalculated continuously from price, shipping, fulfilment method and seller performance.
The consequence for data is that the price attached to a listing belongs to whoever currently holds that position — and that may be a reseller you have never heard of. Recording the price without recording the seller destroys the meaning of the observation.
Ownership changes are a leading indicator. An unauthorised reseller taking the position, or a distributor liquidating stock, usually shows up as a seller change before it shows up as the price move that makes it obvious.
This is why seller identity belongs on every offer rather than on the product, and why a seller change deserves its own event type.
Keep reading
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