When Airbnb was very small, it started with this value proposition of matching people who had logic to offer with people who needed logic. At that time, most people who don't want to stay at hotels and want that these sorts of arrangements would go to Craigslist. So what did they do? They started piggybacking on their rival on Craigslist, increased the visibility for their listings. It was a way of scaling and increasing massively the user base of Airbnb without having to drop a dime on ads.