This article in GrowthHackers explains it pretty well:
What are marketplaces built on? Peer networks? Transparent reviews? Satisfaction guarantees?
Nope, it’s the photos.
Okay, maybe I’m exaggerating a bit when I say that great photography is the critical piece to all successful peer-to-peer marketplaces, but not by much. Don’t believe me? Try buying a car, an apartment, or a mattress on Craigslist without seeing photos of it first and then let’s see how you feel.
taken from the Airbnb article….
Start with the Perfect Experience and Work Backward
As we mentioned in the introduction, after hosting their first three guests in their San Francisco apartment, Gebbia and Chesky began receiving emails from people around the world requesting Airbnb in their own cities and cities they’d like to visit, or as Gebbia put it, “People told us what they wanted, so we set off to create it for them.”  Indeed, much of Airbnb’s growth can be attributed to the fact that—despite what venture capitalists thought—people wanted the service Airbnb offered. One way in which this is apparent is with their approach the photographs on listings. In the summer of 2009, as the company was searching for new office space, Chesky stayed exclusively in Airbnb listings in order to gather firsthand data about the service.  That same summer, Airbnb wasn’t gaining much traction in New York, so Gebbia and Chesky flew out and booked spaces with 24 hosts to figure out what the problem was. As it turned out, users weren’t doing a great job of presenting their listings. According to Gebbia, “The photos were really bad. People were using camera phones and taking Craigslist-quality pictures. Surprise! No one was booking because you couldn’t see what you were paying for.” Their solution was low-tech but effective. According to Chesky, “A web startup would say, ‘Let’s send emails, teach [users] professional photography, and test them. “We said, ‘Screw that.'”  Instead, they rented a $5,000 camera and went door to door, taking professional pictures of as many New York listings as possible. This approach led to two to three times as many bookings on New York listings , and by the end of the month Airbnb’s revenue in the city had doubled. What was stunting growth in New York was also stunting growth in Paris, London, Vancouver, and Miami. This led to the Airbnb photography program, which was officially launched in the summer of 2010. Hosts could automatically schedule a professional photographer to come and photograph their space. Though initially only 20 photographers were contracted by Airbnb, the service became an instant hit.  Though this initiative wasn’t cheap for the cash-strapped startup, the founders felt that the long-term benefits—enhanced listings resultings from this program are two and half times more likely to be booked, and they earn their hosts an average of $1,025 per month—were well worth the cost. By 2012, that number had grown to more than 2,000 freelance photographers employed by Airbnb to photograph 13,000 listings on six continents.