The reason a marketplace competes with its own sellers

A seller builds a category over four years, and then the marketplace launches its own version at a lower price, positioned above the seller’s listing. Nothing was stolen. The platform simply knew which products worked, because it processed every transaction that made them work.

What everyone sees

This reads as betrayal, a partner turning on the people who built the catalogue. Framing it as character misses that the platform occupies a position where the information is unavoidable. Anyone running the same infrastructure would see the same demand curves, and the pressure to act on them does not depend on intent.

What is actually happening

Zhu and Liu studied Amazon’s entry into third-party product spaces and found entry concentrated in categories with higher sales and better reviews — the platform moving into demonstrated demand rather than choosing at random — with affected sellers reducing their own subsequent investment on the platform. Rietveld and Schilling’s review of platform competition sets out the structural version: a firm that both operates a market and participates in it holds a permanent informational advantage over the participants, and complementors respond by withholding the investments that generated the information. The consequence is slower rather than dramatic. Sellers stop launching their most promising products where the operator can see them first.

Why it stays hidden

The conflict hides in the aggregate numbers, which keep rising. Category revenue grows because the platform’s own version sells. What does not appear anywhere is the product that was never launched on the platform, and the seller who now tests new lines somewhere less visible.