I believe those were actually employees, and not someone just advertising the services. They would've had reason to believe that x belonged to y, and that would've been included in the subpeona. Like LoyceV said; the advertisement industry would be absolutely dead if advertisers were held responsible for advertising scams. However, if you advertise an illegal service, that could potentially land you in some trouble. Since a lot of the campaigns users advertise here are legitimate businesses that have been operating for years, this isn't likely to be a concern for many.