Well, when I worked for blockbuster if you were found renting a lot of M games or R movies to those under 17, and enough of their parents complained, that was your job right there. This was for the corporate stores, and about 7 years ago, so don't ask me if the policy still applies. But, considering that it's not even mandated by a law, that seems penalty enough. Hell, you can't even sue Blockbuster for First Amendment rights issues because they have the right to not rent something to however they want as long as the reasons were not discriminatory. And since no one under 18 can rent at blockbuster unless they work there, the reason is "Is it ok with your parents?"