TRAVELLING conmen were put on notice with a joint operation involving police, NSW Fair Trading and immigration targeting a gypsy convention at Cessnock yesterday.

Police and Roads and Maritime Services set up a large random breath-testing and car-inspection centre adjacent to the Cessnock Showground, where about a hundred travellers have converged for a week-long "Christian conference".

NSW Fair Trading officers were hoping to serve court attendance notices on a number of men wanted for conning mostly elderly people out of thousands of dollars. Sometimes dubbed the "bitumen bandits," the gypsies promise cheap driveways but deliver inferior work at inflated prices.

Other common scams involve dodgy roofing, pest extermination and concreting. Within minutes of marked vehicles pulling up next to the showground yesterday, the operation drew an audience of about seven or eight men from the conference keen to see what the police were doing.

The crackdown became a stand-off with Fair Trading officers legally unable to enter the showground and serve those they wanted with papers because the land is privately owned by a trust and the event organisers declined permission.

One of the men in Fair Trading's sights is Thomas Hibbs, who is accused of trying to rip off an 86-year-old Oak Flats man last week.

But it was not known if Hibbs was at the convention.

A Fair Trading officer said the "gypsy season" - September to April - was well under way with an increasing number of English and Irish gypsies returning from overseas.

"They follow the sun. They may have been working their way across Canada and now they're back in Australia," he said.

"This is good reconnaissance for us, it allows us to compile number plates and other data."

More than 30 families with 1000 members have been identified carrying out multi-million-dollar scams, according to a detailed profile of modern "gypsy crime gangs" compiled by Fair Trading.