When suppliers refuse to populate your marketplace, manufacture the inventory yourself by indexing what already exists publicly, then convert the demand it attracts into layered defensibility.
Trulia
Trulia was an online real-estate marketplace, founded in 2005 by Pete Flint and Sami Inkinen, that let homebuyers and renters search listings for free while selling leads and advertising to agents. Its two stories share one through-line: Trulia refused to wait for the supply side to cooperate, manufacturing a full inventory of listings by indexing what already existed, then stacking multiple defensibilities on top of the buyer traffic that inventory attracted.
Cold Start: manufacturing supply by indexing agents' own websites
The problem. In 2005 Trulia faced the marketplace deadlock in its purest form: "How could we attract a consumer audience (homebuyers) without any listings, and how could we attract listings without an audience?" The obvious fix, asking brokers for listing data feeds, was impossible because standardized feeds did not yet exist. The supply was real but locked away inside thousands of individual agent and broker websites.
The approach. Rather than convince agents to upload listings to an empty site, Trulia seeded the hard side without their cooperation. As Flint put it: "Our only choice was to build a real estate specific search engine to index an agent's own listings directly from their broker and agent websites." Trulia crawled and aggregated those listings (handling attribution by sending traffic back to the source site), populating a browsable marketplace overnight.
How it solved it. With inventory in place from day one, Trulia won the demand side through SEO, building rich, search-friendly listing pages that pulled cheap, high-intent organic traffic from Google. That flipped the incentive: no agent had to lift a finger for Trulia to have a full catalog, and buyers arrived because the site was already full. Trulia IPO'd on the NYSE in September 2012.
Network Effect: stacking marketplace, protocol, and data effects
The problem. Indexing manufactured supply, but scraped listings alone are a fragile, easily copied position: any competitor could crawl the same agent websites. Trulia needed the initial buyer traffic to compound into defensibility that a rival could not simply replicate.
The approach. Trulia layered three reinforcing effects. First, a marketplace effect: more listings drew more buyers, which drew more agents wanting in. Second, a protocol effect: "We created an XML feed standard which allowed real estate agents to syndicate their listings to Trulia from their own websites," and listing syndication in real estate was born, turning involuntary (indexed) supply into voluntary (submitted) supply with switching costs. Third, a data effect: user-generated Q&A, neighborhood content, and property edits made the site richer and improved SEO, drawing still more users.
How it solved it. The buyer traffic became the flywheel that made agents choose Trulia rather than tolerate it: "For many agents, we had quickly become the second highest source of traffic to their websites (second only to Google)," so they preferred to syndicate directly rather than wait to be indexed. The stacked effects compounded into a marketplace that Zillow acquired in a July 2014 all-stock deal valuing Trulia at $3.5 billion, creating the largest online real-estate marketplace in the US.