Dennis Helmer says he got his hands on "The List" in the 1990s, while he was working in sales at a long-defunct Twin Cities coin company called National Rarities.
The database included hundreds of thousands of names and phone numbers for established gold and silver customers and others who had expressed interest in precious metals.
Such leads are themselves like gold in the industry, and Helmer knew their value from experience. After his boss at National Rarities was busted for swindling, Helmer said he continued using the list for his own coin sales.
And he found another way to turn it into cash: He sold it to other brokers.
"I called up everybody here locally," Helmer said. "I sold the list for anywhere from $200 to, I think I sold one copy for $4,000."
Though Helmer says he's out of the coin business, his legacy lives on. Versions of the list are traded so widely that many brokers refer to them simply as the "DH leads."
The circulation of the lists has exposed consumers to frauds ranging from high-pressure coin deals to the $194 million Ponzi scheme run by Trevor Cook, a former coin salesman.
Several versions of the customer lists exist. Outdated information is removed, and new prospects are added. Sometimes newer versions get stolen and resold, too.