Zillow and Trulia aren't scraping. The big hole in Zillow and Trulia is listings under contract. A listing goes "pending" (under contract), the MLS knows about

Zillow and Trulia aren't scraping. The big hole in Zillow and Trulia is listings under contract. A listing goes "pending" (under contract), the MLS knows about it right away. Which is why people see Redfin updated quickly -- because as said elsewhere, Redfin displays data from the MLS. Sites like Trulia and Zillow also get data from MLS, sometimes directly, usually indirectly thru other data access deals. And they also purchase access to a lot of public record databases, things like that. So when a house goes pending, these sites don't see that until it closes and becomes a public record, unless the agent themselves updates the listing on the site. Most this is explained elsewhere in this discussion, I just wanted to make the point, though, that scraping isn't part of the process. I'm sure it was early on, but those days are long gone.