We still don't know how Pinterest is going to justify its $11 billion valuation, but we have an idea of how it's going to try.
The online bulletin board introduced a product called Buyable Pins on Tuesday that will let merchants take advantage of the many dresses, shoes, couches and necklaces posted by users. More than 2 million products will be available for purchase when it rolls out to Apple devices this month and Android later this year.
But here's the thing: At the company's big press conference in San Francisco, Pinterest CEO Ben Silbermann said there will be no fees for buyers and no fees for merchants.
Read MorePinterest announces buyable pins
So where does Pinterest make money when a consumer uses the service to buy something from Macy's, Neiman Marcus or Nordstrom?
Silbermann didn't address that question, but the idea seems to be that brands will be able to pay for placement if they want a Buyable Pin to get prominence. In that regard, it's similar to the company's current revenue model around Promoted Pins, which allows brands to create targeted ads in pin form.
Pinterest has raised over $1 billion in venture funding, so it can afford to experiment.
Eventually, investors need to see returns on their capital. For that to happen, Pinterest is going to have to become a significant player in an e-commerce market dominated by Amazon.com, and at the same time compete for ad dollars with Google, Facebook and Twitter.