Which consumer psychology principle did the marketing campaign for 'Harry Potter and the Deathly Hallows' primarily leverage to generate unprecedented pre-orders?

The publishing industry relies heavily on sophisticated marketing strategies and consumer psychology to transform books into bestsellers. Publishers and authors carefully craft campaigns that tap into readers' emotions, create FOMO (fear of missing out), and leverage social proof to drive sales. This poll tests your knowledge about the psychological tactics used in marketing literary works that have helped turn ordinary books into cultural phenomena. How well do you understand the invisible forces that influence your reading choices?

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Scarcity effect - with midnight release parties and limited first editions creating a sense of exclusivity and urgency
Anchoring bias - by initially announcing an artificially high price point before offering 'special' pre-order discounts
Decoy effect - offering three different editions where the middle-priced option was designed to be the most attractive
Social proof - primarily relying on celebrity endorsements and influencer reviews to drive sales