Data from online trading site eBay has helped Centrelink catch out dozens of welfare recipients who are not declaring big profits from internet sales.

Centrelink compared its payment records with the activity of 15,000 people who are running profitable eBay businesses.

It identified 25 people who must repay more than $800,000 in payments they were not entitled to.

Minister for Human Services Kim Carr said about 100 cases warranted further investigation.

"About 25 debts have already been raised, with the average debt amount about $32,000 - roughly double the average debt for other types of investigations over the past two financial years," he said in a statement.

Centrelink general manager Hank Jongen said some matters had been referred to the director of public prosecutions.

"We are not looking at people who are selling their grandma's vase or an old record collection. We are not chasing hobby users," he said.

"What we're doing is identifying people who have deliberately hidden their income in excess of $20,000 a year."

Senator Carr said the Government would continue the online checks as it cracked down on people who were not honest about their circumstances and deliberately defrauded the Commonwealth.

"It's important to point out that the vast majority of people are honest in their dealings with the Government - they are people in need who deserve our assistance," he said.

"However, the take-home message is that if you are seeking assistance from the Government, you need to be upfront about your circumstances.

"If you deliberately defraud the Commonwealth you will be met by a modern and effective compliance system.

"Ultimately, what we want from any compliance measure is to see more money go to those most in need, and this program looks like it will deliver."