In a trial that began on Aug. 19 in San Diego Superior Court, nearly two dozen young women say that they responded to Craigslist ads seeking models and were then tricked into performing in internet pornography. “Wanted,” an ad would read: “beautiful college type preppy girls,” for video and photo shoots.

The ads turned out to be from producers behind a website called Girls Do Porn, who were seeking women to make so-called amateur porn, a style in which fresh-faced new actresses are often paired with seasoned male performers. The trial could last a month, but no matter its outcome it will provide a rare look into a part of the industry that remains shrouded in mystery — often intentionally, by its makers.

Respondents to the Craigslist ads said they were directed to innocuous websites , with pictures of clothed women, that asked for their contact information and photographs.

Instead of being offered modeling jobs, however, they were offered roughly $5,000 to make pornography, they said. But they did it, a number of them now say, based on the assurance, from the producers and their associates, that the videos would be distributed only on DVD outside of the United States and would never be published online.