“He was ahead of his time in recognizing the value of mint-condition cards,” says Ian Donnis, a political reporter for Rhode Island Public Radio and Rosen’s informal mentor, despite being several years his junior. Donnis let Rosen sit at his table during card shows, walked him through the ins and outs of the business and eventually tagged him with the “Mr. Mint” nickname. He’s not surprised that Rosen made a career of it: “[Alan] was good at self-promotion and very knowledgeable about the field … just an irreverent, charismatic, cocky, entertaining person.”

In 1983, Rosen sold his copy-machine business to an associate and went all in on baseball cards. His timing was fortunate: The 1980s saw a card boom, one in which heightened demand for the cards of yesteryear combined with an influx of new card makers (such as Donruss and Fleer) to push the market into overdrive. Rosen says he notched annual sales in the neighborhood of $8 million throughout the decade, topping out at $9 million in 1989.

Even then, he knew it wasn’t likely to last. Some of the newcomers “weren’t making baseball cards; they were making a lottery. And that’s what it is now: a lottery,” he says, referring to the practice of inserting autographed cards and patches of game-worn uniforms into only a few card packs. “They don’t promote the business of teaching and making youngsters care about their product. Now, when a kid doesn’t get the signed card or the special [treat] that’s supposed to be in that box, you know what he does with those cards, right? He chucks them.”

For information about conventions and shows where Alan Rosen will be, visit www.mrmint.com. If you’re interested in doing business with Rosen, call (201) 307-0700.

Another call-waiting beep. Upon his return this time, Rosen sounds distracted, as if his mental wheels are processing something recently heard. “This guy just now, he had 1,000 Harper rookie cards from when he was with the minor league team,” he says, referring to 2012 National League Rookie of the Year Bryce Harper of the Washington Nationals, thought by many within the game to be its next superstar. “But I hate investing in cards.”

That’s not a comment on Harper’s makeup so much as one on the business itself. “There are no more ground-floor opportunities,” Rosen emphasizes, noting how cards featuring top prospects sell for a premium long before most fans have seen those prospects play. The card business hasn’t done much to lure new blood, he believes, adding that longtime collectors have little interest in today’s stars. “They don’t even consider [guys like Harper] a baseball player yet.”

Even as the business evolved away from what it was when he entered it, Rosen parlayed his success into low-grade celebrity, taking out punny ads in Sports Collectors Digest. One featured Rosen next to the roadside spaceship in Mars, Pa., with the caption: “I would go anywhere to buy your cards.” Many others featured his smiling visage and a huge wad of cash fanned out for maximum seductive effect. Unlike many of his wheeler-dealer peers, he made friends and admirers along the way, among them big-leaguers like Pete Rose, Reggie Jackson and Andre Dawson.