At a recent dinner party, Pete Flint, CEO of the online real estate empire Trulia, expressed exasperation with one of his company's largest competitors. While Trulia is better known for real estate sales listings, the rental market has been a growing slice of the company pie since it launched the rental side of its business in 2010. [...] in many markets - notably the dense, high-profile rental markets of San Francisco and New York - the classified listing site Craigslist is its only real competitor. Swapt, a sort of Yelp for apartments that went live last month, hopes that turning the rental market into a "two-sided conversation" will give the company an edge. Consumer habits die hard, and markets need buyers and sellers, making it nearly impossible to compete with something already popular that gets the job done for no cost. [...] because the only way Craigslist organizes its listings is chronologically, in dense markets with quick turnover, it may actually be a more efficient way of searching for new places than a site with more powerful search and more listing information. After 2012 AIM estimates showed a decrease of more than 20 percent in real estate ad revenue, the next year Craigslist added nine cities and a fee of $5 on dealers who sell tickets to concert, theater and sports events, and its overall revenue soared. In August, the company is planning to offer Rental Roost Pro, a set of buttons landlords can add to Craigslist postings that link to bells and whistles such as rental application forms hosted on the Rental Roost site.