We Americans love sports. The teams. The athletes. We just want to reach out and grab them. That is what sports memorabilia collecting is all about. And it is just the kind of passion that sports memorabilia scam artists are counting on.

"When you have this great emotional connection, and you have an ability to easily advertise your wares in a whole host of different ways that were formerly impossible, it makes it ripe for those that are less scrupulous," said Irwin Kishner, an expert on sports law, and a partner and executive chairman at law firm Herrick Feinstein in New York.

One of those less scrupulous people is Illinois auction house owner Bill Mastro, who is the subject of the next episode of CNBC's "American Greed."

Mastro helped to pioneer online auctions of baseball cards and other memorabilia. But unbeknownst to the thousands of collectors who used his services, many of the auctions were rigged. In 2013, he admitted using a system of so-called shill bidders whose sole purpose was to drive up prices and bring him higher commissions. He also tried to pass off a baseball that he falsely claimed was from America's first professional baseball team, the Cincinnati Red Stockings. And in a collector's sacrilege, he trimmed the edges of a rare Honus Wagner baseball card in order to make it look more attractive to bidders. Had they known the card was altered, it would have drastically reduced its value. But Mastro failed to disclose it.

Mastro's scams cheated collectors out of as much as $1 million on paper, though prosecutors say the total losses may never be known. He eventually pleaded guilty to a single count of mail fraud, and was released earlier this year after serving a 20-month prison sentence. His auction house is long gone. But the industry he helped create remains loaded with pitfalls.