Ana Guembes made a quick trip to the Westfield Fashion Square mall in Sherman Oaks, Calif., one recent morning to pick up some face powder at Macy's.

But before she could get to the department store, she was accosted by a salesman at a cosmetics cart in the middle of the mall corridor. "Hello, miss. I want to show you something," he called out to her, brandishing a tube of lotion with Dead Sea minerals. Soon the salesman was applying eye gel, salts and creams to Ms. Guembes's skin while chatting away about their cleansing...