Why does Philip Marlowe specifically asks about these books at rare book shop in “The Big Sleep?”

Question

In The Big Sleep (1946), Philip Marlowe goes to Geiger’s rare book shop. Agnes Louzier — Geiger’s assistant — minds the shop. Marlowe talks to her and says he wants to buy these books:

• Ben Hur 1860: “Would you happen to have a Ben Hur 1860? […] The one with the erratum on pg 116.”
• Chevalier Audubon 1840: “Uh, how about a Chevalier Audubon 1840 — a full set, of course?”

Answer 1

Because he wanted to test Agnes Louzier who was supervising the book store in the absence of Geiger.

We know later that the book shop was not really a book shop but a pornographic place in a disguise.

Philip Marlowe enters the book shop and then the lady asks in a gracious hospitality voice:

“Can I be of any assistance?”

Which is very uncommon for a clerk who maintains a book shop. Her appearance is also odd for a book shop clerk. She was dressed in such a manner as if she was trying to impress customers.

Then Philip asks for the books “Ben Hur 1860 (III Edition) one with the erratum on page 116” and she first asks “First edition?” later for “Chevalier Audubon 1840.”

She replies…

“I am afraid not and not at the moment…”

…respectively for his queries.

Then Philip — in a bit of a surprised and sarcastic voice — says

“You do sell books? Hmmm? ”

This implies that he had known that she knew nothing about books and the place is not a rare book store. This is later confirmed when a person walks into the store and walks straight into the back room.

And — actually — those books are non-existent books. No books with such names exist. Philip made up those names to test her.

This is confirmed when Philip Marlowe walks into other bookstore Acme Bookstore and asks for the same books. The proprietress (Dorothy Malone) there says nobody knows where the books are available because no such books exist.

Answer 2

As is shown in the later scene in the Acme bookshop, these books don't exist (in fact, Ben Hur wasn’t written until 1880).

The scene has two purposes:

• First, to demonstrate that Agnes knows nothing about books (which suggests that the bookstore is a cover for Gieger’s other businesses, opium and prostitution)… – And second, to open up a chance to flirt with the more knowledgeable clerk at the real bookstore, Acme.