(FORTUNE Small Business) – Tom Stemberg has mastered the art of spinning gripes into gold. His latest creation, a chain of children's shoe stores called Olly Shoes, traces its origins to the ill-fitting footwear he found his kids wearing. The seven-unit store, which Stemberg founded in 2001, is beginning a major expansion (with plans for 250 stores within a decade) and expects to pull in more than $5 million this year. "No store carried a broad enough selection of children's shoes, and when the Brannock Device [the standard foot scale] says you're a seven, you're a six in one shoe, an eight in another, and a seven in a third," says Stemberg, 56, chairman of the Toronto-based venture. Olly uses an electronic scanning system to trace a child's feet and match them to pairs in stock. The idea took nine years of gestation: Stemberg interviewed dozens of consumers and then hired a market research firm to quiz hundreds more. "Never make a judgment based only on your own experience," he warns. Stemberg's other rules? Verify that you can make at least a 20% after-tax return on your investment, and find an approach that won't be easy for copycats. To that end, Stemberg made sure his scanning system was protected by patent. --IAN MOUNT