People buying and submitting extra same-sex marriage postal surveys face fines of $2100 or 12 months in prison, said the Australian Bureau of Statistics.
The bureau also warned sharing online selfies could compromise the survey’s individual security.
It comes as a Border man posted on a Facebook page purporting to have four ballots for sale, at $100 each.
The man later conceded he was stirring people up and had not received his survey.
Advocate Eric Kerr, who was raised by two mothers on the Border, said while the survey was important, he believes people are exasperated over the ‘plebiscite’.
“I think people making jokes are doing it out of frustration,” he said.
“I don’t think anyone, voting ‘yes’ or ‘no’, thinks the postal plebiscite was the right outcome, it’s garbage.
“It was forced upon us against our will and the government have left us to fight on our own – it’s frustrating.
“We hope people aren’t selling them or throwing them away, the ballot is important but what the government has done is a joke.”
The Australian Bureau of Statistics said submitting sold Marriage Law Postal Survey Forms would likely be an offence against the Census and Statistics Act 1905 or the Commonwealth Criminal Code.
A spokesman said the bureau contacted several online marketplaces with both eBay and Facebook confirming the selling of survey forms or responses would not comply with their policies and would be blocked or removed.
The bureau also warned people to be careful posting a selfie online with their survey, as marriage equality groups are encouraging.
They said posting pictures online that reveal the unique barcode on their same-sex marriage forms could jeopardise individual results.
The unique barcode, which appears in the bottom right corner of the survey form, is used to link a specific form to an eligible voting Australian.
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Under ABS guidelines, the barcode will register the arrival of a form and is anonymous.
So if a replicated form and barcode arrived first, only that vote would be counted.
An ABS spokesman said while there wasn't a genuine threat of widespread fraud he urged people to take extra precautions to protect their vote.
He said there was no evidence so far of either side collecting barcodes.
"Posting personal information of any sort online is generally ill-advised and this is no exception," he said.
The bureau also said forms could be invalidated by messages or drawings.
“Graffiti, or comments written on survey forms, could invalidate the survey form if a clear 'yes' or 'no' response cannot be determined,” he said.
“Mark just one box on the form with a dark pen and make no other marks on your form to ensure your survey response is counted.”