When the Margaret Preston painting is removed from the auction it is unwrapped. However, a few moments later, when viewed in the bookstore, it is wrapped in brown paper.
Miss Fisher loses her gun during the fight in the bookshop. She leaves the scene without retrieving it, but later she has the same gun again.
The 'ancient Hebrew' written in the margin is actually modern Hebrew script, and the "expert" who tries to read this script holds the page upside down.
When Miss Fisher turns for help in the translation from "old Hebrew" to Mr. Abrahams Sr., he tracks with his finger while reading the phrase correctly right to left (the way Hebrew is read); however, he holds the page itself upside down.
When Phryne checks the lending card catalog after sneaking into the bookshop at night, the volume card lists the name as "Saul Abrahams." This combination is wrong. Saul's last name is Michaels; "Abrahams" is the last name of three other characters unrelated to Saul.
Police detective is shown using a key system telephone, with rotary dial but buttons for other functions, Such phones did not exist until the mid 1930s.