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People selling unwanted or used items on websites such as Facebook Marketplace and Gumtree are at increased risk of being targeted by scammers.
The warning came as the National Australia Bank (NAB) released new customer data today, showing goods and services scams have increased 66 per cent in the past three months.
A third of those reports involved criminals trying to exploit PayID, a free service which uses a mobile phone number, email address or ABN to send and receive money.
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"We are getting reports of people selling an old TV or fridge online and being inundated with identical messages from scammers wanting to purchase the item with PayID," said NAB executive, group investigations and fraud, Chris Sheehan.
"Scammers have realised online marketplaces can be an easy way to rip people off.
"They're also exploiting the fact PayID is a relatively new payment method with money being transferred instantly."
He said the biggest scam red flag was if someone asked you for money to upgrade or access PayID because the service was free.
"There are never any charges related to using PayID," Sheehan said.
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"It's also important to remember PayID will never send you an email, text or message directly as your bank registers and manages PayIDs.
"If you get an email, text or message directly from 'PayID' it is a scam."
Australians lost $260,000 to PayID impersonation scams last year, according to Scamwatch.
How to spot the scam
NAB said the scammers would push to buy your item using PayID, then claim your transaction couldn't be completed because you don't have a "business" account.
They then claim they've sent extra money to upgrade the account, send a fake email as evidence and pressure you to reimburse them but no money will ever appear in your account.
NAB is advising PayID users that the service will never need you to send money to receive a PayID payment.
You will not need to take additional action, like upgrading an account, to receive funds in your account.
You will also never receive communication directly from PayID via email, text or messenger as the payment method is managed by your bank.
