I thought it was strange too. I would suspect the caselaw involving the First Amendment provides more definition of the limits upon governments than the Privacy

I thought it was strange too. I would suspect the caselaw involving the First Amendment provides more definition of the limits upon governments than the Privacy amendments, especially since this is such a novel set of facts with no easily applicable precedent. First Amendment seems to be more broadly protected than privacy anyways, so extending it to this set of circumstances would be ultimately useful. However, their First Amendment argument would be more compelling if the search request was wider instead of specific. It looks like the request only wants a 48 hour period, so its not a dragnet kind of request (i.e., who checked out books on chemistry in the past 4 weeks?). In the event the ruling is against Amazon, I would guess the in camera evaluation will probably happen.