RARE banknotes and coins can sell for thousands of times their face value - and it's always worth seeing if you've got any lying about.
One lucky owner has sold a coin from the reign of William IV for a whopping £30,000.
It was part of The Hethersett Collection of coins auctioned at Noonans Mayfair.
The rare proof crown from the reign of William IV dating from 1831 raked in the highest price during the sale.
It sold for a hammer price of £30,000 against an estimate of £15,000 to £20,000.
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The complete set fetched a massive £184,000 all together and was 100% sold with every lot finding a buyer.
The collection even exceeded its pre-sale estimate of £145,000.
Following the sale Coin Specialist Bradley Hopper said: “The 1831 proof was a fantastic coin and beautifully preserved.”
An Eight Testerns or Dollar struck during the reign of Elizabeth I also sold for £8,000 in the auction.
How to spot a rare coin
A coin is usually classed as rare if a limited amount were struck, or a manufacturing error occurred when they were being made.
A low mintage figure, which is set by The Royal Mint, relates to how many of a coin were made.
Generally, the lower that figure, the more buyers are willing to pay for it, although this isn't always the case.
You can find out what coins are rare and how they look on The Royal Mint's website.
The Change Checker website has scarcity indices too - these tell you how many of a particular coin were minted.
When it comes to error coins, how much you'll get for them varies from piece to piece.
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For example, the HG Wells £2 error coin has been known to sell for up to £1,000 in the past.
Bronze 20p coins have been known to sell for up to £750 as well while error £1 coins have been known to go for up to £200 before.
How to sell a rare coin
You can sell a rare coin on eBay, Facebook, or in an auction.
If you're selling on Facebook, there are risks attached.
Sellers have previously been targeted by scammers on Facebook saying they want to buy a rare coin and asking for money up front for a courier to pick it up.
But it's a ruse to get money out of you and the courier is never sent.
To avoid this happening, it's always best to meet a Facebook seller in-person when buying or selling anything.
Ensure it's a public meeting spot that's in a well-lit area and if you can, avoid using payment links.
'Always take care'
Most sellers prefer to deal with cash directly when meeting to ensure it's legitimate.
The safest way to sell a rare coin is more than likely at auction. You can organise this with The Royal Mint's Collectors Service.
It has a team of experts who can help you authenticate and value your coin.
You can get in touch via email and a member of the valuation team will get back to you.
You will be charged for the service though - the cost varies depending on the size of your collection.
You can also sell rare coins on eBay.
But take into account that if you manage to sell your item then eBay will charge you 10% of the money you made - this includes postage and packaging.
Always bear in mind when selling any rare coin, you will only get what the seller is willing to pay for it.
