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All the situations you mention are where they have a named defendant and are gearing their requests specifically to him. Its would be much easier to go to the library and ask for all the books checked out by a named individual relating to poison. Noone else is getting hurt or being examined. They could surely ask this book store for all books known to have been bought by the individual in this case relating to drug manufacturing. However where the purchase is anonymous, like it probably was here, aka postal money order, cash etc, they can't do so without treading on everyone's rights. There is a big difference between someone who is a named defendant in a criminal case giving up his rights to the state to solve a crime and blanket searching of everyone who has read a certain book.

There is a big difference between someone who is a named defendant in a criminal case giving up his rights to the state to solve a crime and blanket searching of everyone who has read a certain book.

True, but in this case the police were not "blanket searching" for everyone who bought these two books. They were looking for information related to one specific invoice number, plus the 30-day purchasing history of the suspect to whom the "Tattered Cover" package was addressed (the lower court had already nixed the 30-day history search, so the only thing at issue now is the one particular invoice).