I worked in the book trade between 2000 and 2004. I did catch someone's eye once who left the store before putting all the neat piles of hardback books he had stashed under a table in his briefcase.

And I also marked Rough Trade and Lonely Planet guidebooks with invisible ink. After Robert Jordan was arrested I had to identify my handwriting to the police and be available for a court date, but never had my moment in the witness stand... there was no need