Last week Zillow reported earnings and the stock immediately tanked.

Consensus is that revenue growth from its premier agent program is slowing down, and since that represents nearly 75% of the online listing service’s business, investors became skittish.

However, one real estate tech adviser is declaring that those investors are missing the bigger picture in that Zillow is sitting on a goldmine with its latest ventures.

In an email to subscribers, independent analyst Mike DelPrete said Zillow’s strategic shift into iBuying and mortgage lending points to a much more profitable business line. In fact, DelPrete said this shift to focus on seller leads is a “billion-dollar opportunity."

“Zillow's iBuyer business continues to grow, and the latest results crystalize the opportunity in seller leads,” he writes in the email. "Zillow says that since launch, nearly 20,000 homeowners have taken direct action on its platform to sell their home. Of those, it has purchased just about 1% of homes (around 200). That leaves about 19,800 leads who remain interested in selling their homes.”

Zillow could then sell that info to agents on a per-lead basis, or give the leads to premier agents in exchange for a referral fee. But, DelPrete notes this is just the beginning of what Zillow can do.

DelPrete breaks it down:

“Given the value of the seller leads, should Zillow even be in the business of buying houses? Yes, if it wants a credible product for consumers. The real question is: What proportion of houses should Zillow actually buy?

Zillow's "big picture" is 5 percent national market share, which equates to buying around 10 percent of all offer requests (it is currently buying around 1 percent of offer requests). At a 1.5 percent net margin, that's around $1 billion in profit.

But to reach that scale, Zillow would need to spend $68 billion to purchase 275,000 houses annually. Assuming an average holding time of 90 days, it would need a credit line of $17 billion to fund the effort. Big numbers.”

Note: DelPrete is the author of online analysis service, Adventures in Real Estate Tech.