Trade Me members who have usernames similar to their email addresses are easy targets for online scammers, says the online auction site's trust and safety team.

A New Plymouth couple nearly fell victim to an online scam this week after a scammer contacted them about an auction they were outbid on.

David Siddall and Christine Hales said they were bidding on a Toyota van on behalf of their friend on Sunday.

They stopped bidding on the auction after the van went above their $3000 budget, selling for $3425.50 on Sunday night.

The next morning Mr Siddall received two emails from a person named "Albert Cotter" claiming to be the seller of the van and asking for an offer on the vehicle because the winner of the auction had pulled out.

"I actually thought it might have been kosher to start with," Mr Siddall said.

He made an offer of $3000 to the seller who explained that both he and the van were in the United Kingdom and that the van would be shipped to New Zealand free of charge.

It was at this point Mr Siddall realised it was a scam.

"It didn't seem like English was his first language," he said.Mr Siddall said he contacted the original winner of the auction and the official seller of the van and both confirmed their trade was still going ahead.

Trade Me head of trust and safety Jon Duffy said a common activity of scammers was to guess members' email addresses.

Trade Me had warned Mr Siddall on two separate occasions in the past two years that he was at risk of being targeted by scammers because his username was similar to his email address, Mr Duffy said.

If the first part of an email is the same as a username all the scammer has to do is guess the suffix of the email to make contact, he said.

"If they get a hit, they've got you," Mr Duffy said.

In Mr Siddall's case his Trade Me username was the same as the first part of his email address which had a common New Zealand suffix, Mr Duffy said.

"So the scammers obviously just guessed that, made contact with them and tried to perpetrate a scam from there."

Mr Duffy added an additional warning, saying Trade Me users should never deal with people outside the auction.

"Review whether your username is the same as your email address but also don't deal with people you don't know outside the auction process."

Alarm bells should also start ringing if any form of email asks for payment through Western Union, he said.

"That's a huge flashing alert sign that it's a scam. 99.9 per cent of international scams we see on Trade Me use Western Union to move the funds off shore because it's untraceable," Mr Duffy said.

There's also no reason for anyone buying anything on Trade Me to send money overseas, he said.

"The key thing to avoid being scammed is don't ever send money overseas."

Trade Me users can also be contacted by scammers if they leave contact details on a listing.

- © Fairfax NZ News