The bank said a third of reports about the scams related to criminals trying to exploit PayID, a payments platform used by many of the banks.

NAB executive for group investigations and fraud Chris Sheehan said scammers started to ramp up their activities at the end of last year and the problem continued to grow.

He said the bank was getting reports of people selling an old TV or a fridge online and getting inundated with identical messages from scammers wanting to buy using PayID.

They typically tell the seller that the transaction could not be completed because they needed to have a PayID business account or that the seller needed to pay them reimbursement because they had to upgrade their account to a business one to make sure the transaction went ahead.

“Scammers have realised online marketplaces can be an easy way to rip people off. They’re exploiting the fact PayID is a relatively new payment method with money transferred instantly,” Sheehan said.

Scamwatch, which is run buy the ACCC, found this type of scam stole about $260,000 last year but that was likely to be seriously underestimated because many incidents go unreported.

“The biggest red flag of any PayID is often when someone asks you for money to upgrade an account or to access PayID. There are never any charges related to using PayID.”

He said people should pause and think before hitting send on any transaction and should resist being pressured into making a sale. If a seller gets an email, text or message from PayID it is a scam.

“It’s critical to educate yourself about PayID, so you can see through these scams and attempts to find extra money don’t actually end up costing you,” he said.