Craigslist isn't non-profit, it's a for profit business whose goal is user satisfaction, not revenue maximization. For instance, apartment listings are free everywhere except NYC. NYC landlords and brokers asked Craigslist to charge for listings, because it reduced the amount of spam and fake listings. Since users were asking to be charged, they started charging. The money from these few exceptions (like jobs in SV and a couple other markets) makes more than enough money to pay for everything else. They make something like 600-800K per employee, hardly non-profit.