Ah, the ongoing arguement: parents are somehow still woefully ill-informed despite clear legal branding of games as per age groups, and they still buy their clearly underage kids games they're nowhere near mature enough for. [having the rating take up half of the box art though might work,or visible signage on each game shelf, showing the ratings system and the age groups]
But people would more then likely ignore that too
Translation: people are idiots despite intelligent people trying to keeps kids away from mature content, and they still try to blame somebody else for their lacking competence as a parent.
Honestly, people should have a license to have kids, people still clearly buy their kids mature rated games, and still feign ignorance when they suddenly realise what their kids are playing.
The poster above who was a gamestop or ebgames cashier [page 2 i think], i've seen that happen often, people seem to be blind to a clearly marked game, and think somehow their 12 year old is ready for it.
True you cannot refuse a purchase from someone who is of age, but if you could refuse sales on the basis that they're buying for someone underage, people might realise what they're buying.
But we all know that people are just stupid, and lacking knowledge, so we cant do much except deal with it