Think of sports memorabilia, and those baseball cards from childhood immediately spring to mind. It’s simple, nostalgic, a way to hold on to a much simpler time.

Then O.J. Simpson got involved.

Simpson’s arrest almost two weeks ago in an armed holdup of sports memorabilia collectors was a reminder of just how big a business collecting is. And like every business, memorabilia collecting has its shady characters.

“There’s an unsavory side to any business, no matter what it is. It’s the nature of business,” said Josh Evans, chairman and founder of Lelands, an auction house in Seaford, N.Y. “Unfortunately, usually they kind of slip in between the shadows and behind closed doors. When something like this happens, it brings them into the light.

“They’re a very small percentage, only a few.”

According to police reports, Simpson and several other men went to a hotel room at the Palace Station casino in Las Vegas on Sept. 13 on the pretext of brokering a deal with two longtime collectors. But once in the room, the collectors were ordered at gunpoint to hand over items including game balls signed by Simpson, framed awards and plaques and Joe Montana lithographs.

Some of the items were valued at as much as $100,000.

Simpson insists the items were really his and had been stolen from him earlier. But he’s facing multiple charges, including kidnapping and armed robbery.

One of the collectors has a criminal record, as does the man who arranged the meeting with Simpson.

“When you’re not with the flagships of the industry, I’m not real sure who you’re doing business with,” said FBI Special Agent Tim Fitzsimmons, the case agent for Operation Bullpen, which broke up a nationwide network of forgers, authenticators and sellers of sports and celebrity memorabilia.

“It’s kind of like the old axiom, you get what you pay for.”

Although the Simpson case might make the memorabilia industry seem less than legit, Fitzsimmons and others say nothing could be further from the truth. Most memorabilia is bought and sold through agents or auction houses – companies whose multimillion dollar earnings are dependent on doing honest business.

They employ authenticators to make sure that ball really was once hit by Babe Ruth, and the signature on that trading card really is Tony Gwynn’s. If someone brings them something to sell, they require a provenance, a paper trail that traces the item’s owners and history.

“You won’t last long in this business unless you’re being fair with people,” said Dan Imler, managing director of SCP Auctions, which recently auctioned off Barry Bonds’ 756th home run ball.

“It’s all about earning people’s trust and earning your future business. Generally, those people that are unscrupulous don’t stick around long.”

A problem the industry does have is with forgeries or fake memorabilia. Before Operation Bullpen, the FBI estimated that much of the “vintage” memorabilia – pictures, autographs, bats, balls – were fake.

Athletes would come across autographed pictures of themselves and have no idea whose signature was on it. Jerseys passed off as authentic were no more unique than the ones on sale at the mall.

“There were one or two of them that were just people running a criminal business out of their bedroom, more or less,” Fitzsimmons said of those arrested in Operation Bullpen. “If you’ve got a computer and a pen and a bunch of items to forge, you’re in business.”

But as the FBI was conducting its investigation in the late 1990s, athletes, sports leagues and collectibles dealers began taking action of their own.

Items were marked with unique, tamperproof markings to ensure their authenticity. When Barry Bonds was chasing Hank Aaron for the all-time home run record this summer, Major League Baseball used specially marked balls for Bonds’ at-bats. Thirty years from now, there will be no question about whether a ball really was No. 756 – and not because the guy who bought it has decided to stick an asterisk on it.

Auction houses and dealers employed authenticators to make sure pieces were legit and signatures were real. Athletes signed with companies so there would be only one source for their memorabilia. Want an autographed picture of Tiger Woods winning the 2006 British Open? Unless he gave you one himself, you’ll have to get it from Upper Deck.

“I would say the majority of stuff out there being sold directly to the public, the majority is authentic,” said Doug Allen, president of Mastro Auctions in Burr Ridge, Ill.

“It’s not bad auction houses out there,” he added. “What there are is bad people trying to get things past auction houses and authenticators. Do you have any idea of how many Babe Ruth baseballs we turn down? A lot more than we sell.”

One ugly incident like Simpson’s, though, and the whole sports memorabilia industry is suspect again.