Thurman Munson, the great Yankee catcher, was killed in a plane crash in 1979. Bobby Brown became president of the American League in 1984. A baseball with the seal of President Brown and the signature of Munson is impossible, but that's exactly what some guy was trying to sell through the online auctioneer eBay Inc.

Rob Chesnut, associate general counsel for eBay, telephoned the seller to determine whether he was pulling a scam or merely naive. The man couldn't explain the difference in dates. Nor did he seem embarrassed or surprised that he was selling a fake, which would have been an innocent person's reaction. To top it off, Chesnut knew the man had been bidding on his own auction to jack up the price, an eBay no-no.

"We can't tolerate forged or fraudulent items," said Chesnut. "I'm going to suspend your account."

With that, he clicked his mouse and banished the man, immediately making the auction site a little safer for law-abiding folk.

Chesnut is the eBay prosecutor, judge, jury and, when need be, its executioner. Some days, he gives the boot to as many as a dozen people. The rest of the time, he's writing the laws for this burgeoning online community.

A few years ago, when Chesnut was still a federal prosecutor in Alexandria, the Internet was famous as a place where there were no rules, where you could drop your real-world identity and masquerade as whomever you wanted.

It was the Wild West all over again, with law enforcement often uncertain what the Internet was, much less how to track wrongdoers. E-commerce was so new that people were terrified about providing credit card information. Any deals were private negotiations between two parties, which meant caveat emptor.

As the Internet has become increasingly commercialized and positively suburban, the enforcers and legislators have arrived--nowhere more so than at eBay, where the company is the final authority on tens of thousands of transactions a day. Other consumer e-commerce companies watch eBay so closely that, according to Chesnut, they frequently plagiarize wholesale its user agreement--right down to the typographical error.

Chesnut recently prohibited the auction of bear claws, material from Cuba (unless it's art), stuffed migratory birds, police badges (even movie replicas), shares of stock, Native American masks, cigarettes and cigars, bottles of wine, human sperm, firecrackers, wild mushrooms, roach clips and bongs, TV descramblers and gravestones, and he's pondering what to do about used makeup.

"We all need rules to live by, and the Internet's no different," said Chesnut. "We're posting new rules all the time."

When eBay began four years ago, founder Pierre Omidyar envisioned it almost like a club, a place where people could informally buy and sell small items of value. As a business, it was low key; Omidyar ran it out of his home. But the notion quickly caught on, with some people using eBay to empty out their house and others to fill theirs up.

At one point earlier this week, there were 3.36 million items registered for sale in 2,568 categories, such as vintage cap guns, thimbles and McDonald's memorabilia. The number of registered users, 7.7 million, is greater than the population of Chicago and Los Angeles put together.

The company's employees, most of them in a low-slung building in an anonymous office park here, never see any of the objects being sold. With 350,000 new items being listed every day, it would be difficult for eBay to screen them ahead of time. It doesn't even try.

In its lengthy user agreement, eBay makes clear that it does not vouch for the authenticity of any transaction. But as a publicly traded corporation with an astronomical market value of $19 billion, it needs a good reputation--and as much new business as possible. The safer it is, the more it is likely to have both.

Enter Rob Chesnut. Until early this year, he was supervisory federal prosecutor for Helen Fahey, U.S. attorney for the Eastern District of Virginia. He handled many high-profile cases, including Russian spies Aldrich Ames and Harold Nicholson, and was well-liked by his boss. But newly married and approaching 40, Chesnut was a little restless.

He had a small business sideline of artistic photography, which required camera parts and accessories that weren't easy to get. A photo magazine led him to eBay, where he typed in "Polaroid" in the search box. Expecting to see only a few items, he was astonished to find 300.

He became an eBay regular. While bidding late one night, he thought: "With millions of transactions, they could probably use someone with a legal background. Maybe even a prosecutor." Before he went to bed, he e-mailed his re{prime}sume{prime}. The next day, the company called.

For the first 2 1/2 years of its existence, eBay had no lawyer on staff. The first one was hired in early 1998; the second, a general counsel, right before it went public that September. Neither had a law enforcement background.

User complaints about fraudulent behavior were handled by the eBay staff, but this mostly consisted of telling aggrieved customers to contact the police themselves. These days, there's a whole fraud unit that is proactive as well as reactive.

"Rob was the lone sheriff initially, but that's ridiculous--you need an entire department," said Angela Malacari, who came to eBay in June to run what is now called the Fraud Prevention Department.

A former Immigration and Naturalization Service agent based in Alexandria, Malacari's knowledge of Chesnut goes beyond the professional: She's his wife. "It's like that old TV show, 'Hart to Hart,' where the husband and wife are the investigator and the attorney," she said with a laugh. "We're a real law enforcement family."

Both Malacari and Chesnut stress that the actual amount of fraud committed on eBay, whether it's knowingly selling forged or illegal items or collecting cash for an object and then not delivering the goods, is extremely small. Still, dozens of auctions are stopped every day by eBay.

Malacari, moreover, feels that the Internet "is where crime is going. There's more anonymity. You can assume someone else's identity. The bad guy is not hiding on the streets, he's hiding behind his screen at home. It's a new specialty for law enforcement."

The eBay transgressions that get the most publicity are those that involve body organs, such as livers and kidneys. In a somewhat related vein was the young Florida man a couple of months ago who was supposedly auctioning his virginity. He, like the organ sellers, was referred to authorities; in his case, for prostitution.

It's unclear how many, if any, of the attempted sales of body parts were genuine; Chesnut says the police don't report back to him. His guess is that many of them were hoaxes. Then there was the fellow who placed his entire company for sale. In that case, there was a picture of the building, and a request from the president of the firm for initial bids to exceed $10 million.

An attorney for the company found the auction and alerted eBay that it was a fake. The perpetrator, who had his account suspended, was a disgruntled employee. Hoaxes have declined since eBay last month started requiring all sellers to provide a credit card number.

Even for the more professional criminal, eBay is often a very stupid place to commit a crime. But then, some crooks are just dumb. There recently was a case where someone whose house had been robbed checked on eBay and saw his property for sale.

"Things go on in the real world, in a flea market or pawn shop, that no one notices," said Chesnut. "But at eBay, the eyes of the world are watching."

The world, in fact, is watching more closely than eBay management. Usually, the first notice of an illegal or fraudulent item is a complaint by a user. The auction house has instituted a Community Watch program, turning its customers into its police force.

Coin buffs wrote in about an auction involving an 1879 C.C. Morgan mint proof, worth at least six figures. The picture of the coin on the site included an authentication number that looked as if it had been crudely tampered with. Chesnut contacted the Secret Service, which investigates counterfeiting. A search warrant confirmed the fraud.

As the world of eBay grows almost as multifaceted as the real world, people are always finding new things to sell. Last May, users noticed that several individuals were selling old tombstones on the site. Outrage immediately followed from genealogists, who worried that graveyards everywhere would be desecrated.

"After repeated objections from our group of genealogists, [you] allowed a federal military grave marker from Indiana to be listed," wrote one man. "I have had my fill of your arrogance. Accordingly, I am filing a legal request through the Indiana Consumer Protection Bureau to the Indiana State Attorney General requesting that you make your presence in Indiana to answer charges of racketeering and the breaking of federal laws restricting the interstate sale of stolen goods from the State of Indiana."

The sale of gravestones on eBay was quickly banned, but the episode still garnered Chesnut a death threat, as well as a separate promise that his grave would be "a vile, disgusting place." Aldrich Ames was never so upset.

But then, eBay always provokes fierce emotional reactions among its users, and Chesnut now bears the brunt of it. "I think he's been surprised at how high-profile the job has been," said Fahey, his old boss. "He's become a lot more famous out there than he ever expected or intended."

Despite the attacks and grumbling, most eBay users are incredibly loyal. Competing auction sites at Amazon.com and Yahoo haven't been able to gain much traction. Unfortunately, even the crooks are loyal to eBay. Knock them off and they pop back up under a different name.

"At least when I was a prosecutor and the person went to jail, I didn't have to worry about him escaping and then having to track him down and put him back in again," said Chesnut. "But in this environment, once you've suspended someone the job has just begun."

In extreme cases, eBay has filed suit against users who are thrown out but keep coming back. The record for reappearances is 157, by a user in Japan who keeps harassing one particular seller over a deal gone bad. The runner-up, at 113, is a dealer in bootleg music.

All this means that the number of eBay regulations, as well as the staff to enforce them, will continue to grow.

"The day where I can kick back and play golf and let my rules take over won't come any time soon," Chesnut said. "We're hiring another lawyer right now."

CAPTION: "We all need rules to live by," says eBay's Rob Chesnut of his online job.

CAPTION: Enforcing online auction rules is a high-profile job for Rob Chesnut.