Though how they do it isn't obvious, service Web sites do generate revenues and theoretically should be able to turn a profit at some point. Search engines may also license their content to other search engines and make money that way. Or they may charge fees to companies that want their listings highlighted. Sites with affiliate programs essentially turn other sites into sales reps for a small commission. An affiliate site has a button that lets a visitor go elsewhere to buy merchandise.
Affiliates get a commission on anything their visitors buy from that site.
The button generates revenue and is considered a marketing plus for the site that hosts it. This is also an increasingly controversial business because of actual and potential abuses of private information. Many consumers are already wary of shopping online for this reason, and there is pressure on legislators and governments to regulate the sale of personal data. The detailed demographics and information on buying habits and personal interests are a gold mine for companies that want to do niche marketing. And if a site has 1 million registered users, it could sell and resell its demographic data on them for years.