Unscrupulous scammers are attempting to fake 'error' versions of the new 12-sided pound coins and sell them for inflated sums on eBay.
In some cases, all or part of the centre silver area is missing from the coin, in others, the queen's head is on the wrong side, or else blank and shiny. Sellers are asking anywhere from £3.50 up to £20 for these coins.
However, they are actually worthless, says Chris Perkins of the Check Your Change website.
"It's fairly easy (so I hear) to push out the middle part of the new £1 coin and the same for the £2 coins. Anyone that does so and tries to fool people into thinking it's some kind of error and was made that way, either by describing it as such, not describing it at all, or claiming to innocently know nothing about it, is clearly of very dubious character. People that break coins are also committing a crime," he says.
"Genuine error collectors know what genuine error coins look like and always understand exactly what went wrong during production."
So what should you look out for?
There are already hundreds of millions of the standard 2016 coin in circulation, and hundreds of millions more are being minted dated 2017. These, of course, are worth only their face value of £1.
However, there are rarer versions to be found. Around 235,000 'trial pieces' dated 2016 were minted for loan to vending machine companies, and many are believed to have made it out into circulation.
And according to the Check Your Change website, at least two coins have been found that have the standard 2016 design on one side, but the 'trial piece' design on the other - making them likely to be pretty valuable.
Another of these so-called 'mule' coins consists of the standard 2016 design on one side and the standard 2017 design on the other. About 50 have been reported so far.
Finally, there's the 'Brilliant Uncirculated' pair of coins, minted last year and with a cross crosslet mark below the left side of the crown. Around 10,000 of these will be made.
And there are some genuine error coins out there, says Perkins.
In one, known as a partial collar error, part of the outer rim lacks the ribbed texture, and splays slightly outwards to form what appears to be a raised lip around the edge.
In the other, it looks as if the collar, or mould, has broken during the minting process.
"Metal has splayed out upon strike impact and this has caused a little chain reaction with the silver coloured centre part being pushed to fill the void in the brass outer part," says Perkins.
"On extreme cases the movement of metal has caused a gap between the outer ring and centre part of the coin."
So far, he says, quite a few have been found - and could be valuable to collectors.