In 1973, Louis Oliari opened Coins ’N Things, a small storefront between a Dairy Queen and a hair salon in Brockton, Mass. His teenage son Mark had become obsessed with coin trading, and Louis, an engineer and a coin enthusiast himself, figured if he indulged the kid he’d eventually outgrow the hobby and go to college. “The whole idea was that I’d get bored and get this out of my system,” Mark, now 54, remembers.

Today, Coins ’N Things is the largest seller of raw gold to the federal government. In the fiscal year that just ended, the U.S. Mint, which has bars made into coins for collectors and investors, bought $1.86 billion worth of the metal from the Bridgewater (Mass.) company. Not too shabby, considering that Coins ’N Things and the Mint struck their first deal less than two years ago.