Craigslist offers listings for everything from apartments to lawyers to dates. It is free for users to search and in most cases, free for posters to put up their ads.
Patricia Nakache, a general partner at the venture capital firm, Trinity, is backing start-ups that figure people would be willing to pay for higher-quality, screened listings.
Because Craigslist does not much care about making money, it can be hard for a profit-driven business to compete. Just ask newspapers, which have seen their classified ads virtually disappear. But Ms. Nakache argues that “people are willing to pay for a better experience.”