Prostitution
Prostitution is undeniably a symbol in this book, but its interpretation shifts depending on whose opinion is being elicited. Obvious Madam Willie doesn't really object to prostitution, having become a powerful business in the industry. Her mother doesn't mind, because it's easy money, but Josie hates it. Josie sees that they are judged, and her hopes of having a normal life seem like a far shot from her daily life cleaning up after her mother and other prostitutes, and the messes they make with their "clients."
The murder
When a wealthy patron of Patrick's bookstore ends up murdered, Josie thinks her mother might be involved. This is a symbolic realization, because whether it's true or not, it helps to show that although Josie mostly feels ashamed about prostitution, the real reason she doesn't respect her mother is because she doesn't trust her. Josie thinks her mother is absolutely the kind of person who could murder someone in cold blood for a fat check. This symbolizes Josie's awareness of her mother's sociopathic, self-interested ways.
Patrick, college, and independence
Patrick represents the hope for the future, because he is attractive to Josie, and also because he literally sells her books, which point forward toward her college hopes. In the end, this entire friendship ends up being a symbol for Josie's commitment to doing well for herself. Josie is determined to earn independence through hard work.
The motif of shame
This book is like a museum of shame. Each character has a shady backstory, but the most obvious and important use of shame is Josie's name, her mother's occupation, and Josie's day-job (she cleans up after the sex workers between Johns). Josie is slang for prostitute in Josie's community, so that adds an extra level of awareness to Josie's shame, shame that she feels not because of what she does (although she is embarrassed to be a brothel janitor) but rather, Josie feels ashamed about who she is, about who her mother is, and about their station in life.
The symbolic climax
When Josie decides not to follow her mother's example, it's clearly symbolic, showing that to the best of her abilities, Josie intends not to repeat her mother's mistakes. Now, ideally, she wouldn't have to despise her mother to make that choice, and after all, she does experience the temptation of prostitution—she's young and sexually curious, and she has a serious need for money, but that's exactly what makes the moment so powerful. She succeeded in differentiating herself from her mother, at least in this way.
