The body overseeing the postal survey on same-sex marriage is working with online sales sites to take down listings of those trying to sell their ballots.
Deputy Australian Statistician Jonathon Palmer says some auction items have been blocked before they've gone online.
He estimates the number is less than 30 and says others have been removed promptly.
"It seems everyday or two someone has a crack at listing a form," he told ABC radio on Wednesday, thanking eBay and Gumtree for their co-operation.
"I think it's a bit of a joke frankly."
All survey forms have now been lodged with Australia Post, with the last 20 per cent of ballots on their way to households.
If people don't receive theirs by September 25 they are encouraged to contact the Australian Bureau of Statistics.
Mr Palmer defended the work of the bureau and Australia Post.
"When you send out 16 million forms I'm sure there is going to be a few incidents. I think it is running smoothly," he said.
All forms need to be received back by November 7, with the result to be published on November 15.
