Buy box
The seller offer wired to the main buy button when several marketplace sellers share one product page.
See it
What it is
A buy box is the seller offer attached to the main purchase button on a marketplace listing shared by several merchants. Amazon calls its winner the Featured Offer. The product page may represent one catalog item, but the price, delivery promise, and seller behind Add to Cart come from the offer that currently owns that slot.
Build one when several sellers can offer the same catalog item and you need a useful default instead of making every shopper compare a table. Eligibility and ranking can consider total price, stock, delivery speed, fulfillment method, and seller performance. Other eligible offers should remain reachable.
Gotcha: winning is not the same as having the lowest sticker price. Shipping can change the cheapest delivered offer, and a fast, reliable seller may beat a cheaper one. Never present the ranking as permanent: stock, price, and delivery estimates move, so recompute it from current offer data.
Ask AI for it
Build an Amazon Featured Offer-style buy box for a multi-seller marketplace. Store offers separately from the shared catalog product, then filter out offers with no stock or suspended sellers and rank the rest by delivered price, estimated delivery date, fulfillment method, and seller service score. Render the winner beside the main Add to Cart button with seller, item price, shipping, total, stock, and delivery promise. Add an 'Other sellers' panel sorted by delivered price, and recalculate the winner whenever an offer, inventory count, or shipping quote changes. Keep the scoring weights in named server configuration and return the winning offer ID from the server so the client cannot appoint its own seller.