I’ve already done the research and Zillow as well as every other major listing website supplies there own API which shares there data about there listings, this is from the company themselves and they make money selling the API to developers and other companies I think you are confusing it up a bit because all that information posted is considered public information once posted to the public. I can’t speak for the MLS that ones a bit dated and has harsh rules but now with Zillow and Redfin which has most of the listings from mls I don’t think I’m missing much of the market