'They included several students,' he said. 'The youngest person was a 16-year-old high school pupil.'

He said about 40 per cent of the 34 people customs arrested in 26 cases last year were aged below 30.

'The investigation showed that about 60 per cent of people arrested this year had decent occupations and they sold fake goods through auction sites in their spare time,' Ho said. Last year, the majority of the offenders were jobless.

This year, customs officers also noticed that fraudulent online traders changed their delivery method in an attempt to avoid detection.

'[Counterfeiters] are now delivering goods by post instead of coming out to complete their transactions face to face,' Ho said. 'I think they want to lower their risk of being arrested by customs.'

Since 2005, auction site operators have removed about 80,000 listings of suspected counterfeit goods.

But the number of complaints about counterfeit goods being sold on online auctions rose by about 17 per cent this year, according to the Customs and Excise Department.

The department received a monthly average of 33 complaints about such illegal activities this year. Last year, it received an average of 28 complaints a month.

'Some of the offenders don't think it's a crime and they don't think customs can catch them because so many people use the internet every day,' Ho said. 'With the co-operation of internet service providers, we can easily track down sellers of counterfeit goods. This is not difficult for us.'

Because of the growing number of complaints, the department launched an operation on November 25 to combat internet auction site sales of pirated goods.

About 100 customs officers have posed as buyers, made purchases on the internet, identified sellers and gathered information around the clock for the past two weeks.

During the operation, customs seized 546 fake brand-name products with an estimated market value of HK$170,000.

Those arrested - seven men and 12 women - included nine employed people, two students and two housewives. They have been released on bail. Among them were an 18-year-old schoolgirl and her mother, who were accused of selling counterfeit sunglasses.

'The mother is a housewife,' Ho said. 'It is alleged that she bought counterfeit goods and her daughter sold the fakes through an online auction site.'

He said most of the offenders operated individually and no evidence suggested they were controlled by an organised syndicate.

The price of the fake brand-name products such as handbags, wallets, sport shoes and accessories was about 10 per cent of the original value of genuine products.

'The profit margin is roughly between 10 and 20 per cent,' Ho said. 'It is not worth doing this because we can catch you.' He said customs would continue the operation during Christmas and New Year.