Screeners server a couple of purposes. Routinely, wholesalers or retailers will get a screener which supposedly allows them to decide how well a given title might sell or rent. Personally, I never believed that anybody would be capable of viewing more than a small percentage of the videos that get released, but I guess they have their place as promo tools.
But if you've actually bought one, then somebody should get in trouble. Those things are freebies only, not for sale to the public. $6 for a new DVD isn't bad, but its still a scam since they're free to the retailer.