In Norse mythology, which retail-related concept did Odin use to maintain 'customer loyalty' among his warriors that has become a fundamental principle in modern brand loyalty programs?

Throughout history, myths and folklore have contained surprising insights about commerce and customer relationships. Ancient stories often featured marketplaces, treasured goods, and loyalty to craftsmen that mirror modern retail concepts. This trivia question explores how mythological retail practices influence brand loyalty concepts we still use today. Test your knowledge of how ancient wisdom connects to contemporary customer retention strategies!

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Valhalla's exclusive membership (only the worthy could enter, similar to tiered loyalty programs)
Brisingamen's daily discount (Freya's necklace offered decreasing value each day, encouraging immediate purchases)
Thor's hammer warranty (Mjölnir came with a lifetime guarantee, establishing trust in craftsmanship)
Loki's price matching (he would transform into competitors to learn their prices, then beat them)