Should a sister ask her sister to return books containing bad things before she returns from her trip, or should she read the books and avoid what is bad in them, and what should she do if the store does not accept their return?

If the books are beneficial, there is no harm in acquiring them and benefiting from them, while avoiding error. However, if they are books of magic and sorcery or promote evil, then it is not permissible to buy them.

If your sister has bought forbidden books, advise her to return them and get her money back. If they cannot be returned without returning the books, then she should retrieve the money without returning the books, so as not to promote their false content.

It is permissible to destroy forbidden books such as books of disbelief, magic, astrology, and sorcery, due to the prohibition of engaging with them. It is also valid to buy books of heresy in order to destroy them.