She Knew Them All
Alicia was friendly with all the regulars, that is what happens once you see a person once a week for years, and she had them all figured out. She could immediately tell you who would debate with her over the price of a rare antique and who would happily pay the displayed price.
Not many people lived in her town, so she essentially knew everyone. So when a strange man waltzed into the store one day, she knew she needed to keep a watchful eye on him.