TravelPony relies on users sharing hotel deals. Users access the site via their Facebook login for hotel deals. The prices are competitive thanks to users’ willingness to share a post on their Facebook or Twitter. Once they’ve booked the hotel, they share the deal via the same social media ie indirect marketing. Although not compulsory, it works probably because of the community spirit and it’s an honourable thing to do since it was through the community that they got better prices. So, whilst competitors spend on marketing they rely on word of mouth via social media. Saving on their marketing budget should, in turn, allow them to pass on savings in their hotel rates, thus hopefully helping to generate even more social sharing.
Send an email to me, firstname.lastname@example.org and I'll reply with further examples. Or if you know of other interesting methods, let me know. I'll compile and make another post. I also welcome your thoughts, interpretations or disagreements.