Which retail innovation, introduced in 1916, fundamentally changed shopping by allowing customers to select their own merchandise without clerk assistance?

The retail landscape has evolved dramatically throughout history, with many innovations that fundamentally changed how people shop. Some retail pioneers introduced concepts so revolutionary they permanently altered consumer behavior and business practices. This trivia question focuses on a significant historical retail innovation that transformed the shopping experience and set the foundation for modern retail concepts we take for granted today.

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Piggly Wiggly's self-service grocery store model
Woolworth's fixed-price merchandise system
Sears Roebuck's mail-order catalog
Marshall Field's department store return policy