The Casual Vacancy - JK Rowlings new book

JK Rowling's first post-Potter book is being released today and judging by the reviews and descriptions of the content it's not one I'll be purchasing.

This is being described as her first 'adult' book except how would that be enforced? Sure it's not going to be included in the children's section, but it is going to be displayed prominently in the leader sections and if her name is prominent enough (which it is) how many young readers of the HP series are going to nag parents into buying it for them?

Will shop assistants point out it that it's written for adults, that it contains a rape scene?

Oddly enough books don't come with age-certification excepting some comics that (like some music albums) declare they're for mature readers only. So how would this adult book be sold?

I suppose it's a burden on any pegged children's author, but I am curious as to how it's resolved.