By Mark Ward
Technology Correspondent, BBC News website
Few firms embody what the net is all about more than eBay.
Ebay now has more than 100 million users
The auction site brings together strangers with similar interests, relies on them to act honestly and honour their commitments even though the two parties may never meet.
Probably more than any other business, the trustworthiness of eBay's users dictates the public perception of the company.
That role of honest broker has become even more important as eBay has grown.
Now more than 100 million people have an eBay account.
"We started as a very collector-oriented business," said Gareth Griffiths, head of trust and safety at eBay UK.
"But now significantly less than half of deals are collector goods," he said.
EBay recommends that people don't use money transfers
"The segments we are tapping in to are changing accordingly," he said.
"We've moved on from the very tech smart, early adopter types who understand a lot more and are less worried about the risks because they know what they are."
Increasingly the average eBay user is the average man, or woman, in the street.
As a result the average eBayer is more interested in winning auctions or flogging their own stuff than they are about security.
It is a situation that some criminals are trying to exploit.
"The fraudsters are going after the weak link and that's not the company," said Mr Griffiths.
Mr Griffiths said people should exercise the same amount of reasonable judgement and common sense online as they would in the real world.
But, he said, people do get caught up in the whole online experience and suspend the wariness that helps stop them getting caught out offline.
Many people ignore warning signs that, when they later reflect, should have spelled trouble.
"When we talk to people almost always they say they took a chance and it screwed up," said Mr Griffiths.
Warning signs such as an eBay user who does not have much feedback, has only bought rather than sold before and insists on payment by Western Union should all ring alarm bells.
EBay's links with the police has led to fraudsters being arrested
"Even Western Union say don't pay by Western Union," said Mr Griffiths.
In such cases eBay can do little to help.
"If you do these things then we cannot help you because you have taken it off our site," said Mr Griffiths. "We do not know who paid whom or any of the details."
One trick that some fraudsters are trying is fake second chance offers.
Typically these are sent to someone who just missed out on winning an auction and offer more of what they were bidding on.
"If you look very often it is a completely different seller, different ID and not the guy you bid with," he said.
In these, as in all eBay auctions, said Mr Griffiths, it is worth paying attention to the details of who is contacting you, what they are offering and the price.
Those who are suspicious can send information to email@example.com to check someone out, see if an e-mail message they have been sent is a phishing attack or if a website they've been told to visit is legitimate.
Also available is the eBay toolbar that turns green when users are on a legitimate eBay website.
EBay has very close links with regional police forces that help to shut down phishing and fraud gangs. Recently a 20-strong group of fraudsters was arrested in Spain.
Mr Griffiths said eBay tries hard to educate people about dangers and it is part of Project Endurance which will be three-year, £2m campaign to get people using the net safely.
In the real world experience shows us how to behave safely, he said, so much so that we do it intuitively.
"But," said Mr Griffiths, "the internet is brand new and, so far, we don't know how to behave intuitively."