Mystery shopping has spread from retail to many service-oriented industries, including hotels, banks, and even doctors' offices. Meanwhile, its services have expanded. Lynne Brighton, senior vice president at Bare Associates, says her firm now offers "intercept interviews" with customers on their way out the door, "internal customer" (or employee) interviews, and comparison reports of a client's competition.

When Kathy Romero, director of surgical services at St. Mary's Health System in Knoxville, Tennessee, wanted to know how patients perceived their hospital experience, she turned to Beverly Gleason and her local firm, Mystery Shoppers. "I knew they expected competent surgeons and up-to-date technology. But I wanted to balance that with personal attention." She's glad she did. Patient feedback helped her figure out some simple improvements: Offer current waiting room periodicals, name tags for staffers, and introductions to the doctors and nurses. "There aren't any tools that capture patient satisfaction like this," says Romero. For $50 to $100 a visit on average, mystery shopping firms provide write-ups based on an assigned shopper's observations. But watch out: The industry is still young and working out its kinks. Mark Michelson, president of the Mystery Shopping Providers Association, points out that plenty of fly-by-night firms give little more than passing or failing grades, as opposed to detailed and useful assessments.