Fraudsters targeted around 6.9 million people in the UK in the last week alone, research reveals.
And half of those lured by scammers will have ended up losing their money.
See also: New Aldi voucher scam warning
Clever crooks can con victims out of thousands of pounds in minutes by tricking them into giving out personal details or paying for nonexistent goods or services.
"Scams work because they are difficult to spot," says Gillian Guy, chief of Citizens Advice, which carried out the shocking survey.
"As well as looking for common signs of scams, it's important you take steps to protect yourself when making purchases – such as paying with credit or debit cards which offer greater protection if something goes wrong."
Despite losing large sums of cash, two-thirds of people who have been targeted in the last two years did not report the crime.
The only way to fight these crooks and try to get stolen cash back is to report them immediately and get them closed down.
Gillian adds: "If you think you've been scammed, report it straight away so authorities can investigate and you can get advice on whether you can get your money back."
5 most common tactics used by criminals
1. Fake services
Fraudsters pretend to deliver a service, or send people an invoice they think they're obliged to pay, such as for tax. The most common fake service reported to Citizens Advice was computer virus repairs.
How it works A scammer will contact you, usually on the phone, offering a sham service. In an added sting, crooks will try to obtain your personal details while carrying out the service or arranging payment.
When it comes to computer virus scams, fraudsters gain access to your machine remotely and to your bank account details.
What to look out for: Unexpected phone calls, "sales people" offering time-limited deals, being offered a service immediately or being put under pressure to pay now. Also be wary of unsolicited letters or emails asking for payments.
Average loss: £2,751
2. Phantom goods
Rogues dupe people into paying for items that don't exist. Citizens Advice says the number of shoppers being swindled this way has risen 17%. The most common items were cars, flights and furniture.
How it works Crooks advertise cut-price stuff on social media sites such as Facebook and Instagram and online marketplaces such as eBay and Gumtree. They make products look convincing by creating professional looking websites and posting fake reviews so they appear to be from a reputable trader. The buyer purchases the item, which then fails to materialise.
What to look out for: Being asked to pay by bank transfer, or being sent a link to a payment page which can easily be faked. Keep an eye out for websites that don't have a full postal address and phone number when you do a domain checker on whois.com.
Average loss: £1,100
3. Upfront payments
Don't fall for it
Conmen get people to pay a deposit for a service and then disappear before the job is due to start. The most common scams involve building work, and being asked to pay a fee to take out a loan.
How it works Cheats pose as a tradesman or other professional. They ask for a fee to be paid in advance – perhaps saying they need to buy materials first. Once they've received the money they disappear without trace.
What to look out for: Be wary of a seller or tradesperson who turns up uninvited on your doorstep, and anyone who won't give you references from other clients or the name of the trade body they belong to.
If they have a website, make sure they provide their full name and contact details. Also be cautious of being asked to pay an admin or release fee with a bank transfer.
Average loss: £3,421
The scam may not be anything to worry about however
Cold-calling cheats who try to obtain your personal details. They are most likely to pretend they're from a phone blocking service, debt management company or a bank.
How it works Criminals impersonate someone from an institution, such as the police, bank or government body.
They get you to share your card or bank details by telling you that your identity needs to be confirmed or you need to make a payment.
Once they've got your details they can help themselves to your cash.
What to look out for: Being cold-called and asked for your personal details such as account numbers, credit card details and PINs or passwords. A legitimate organisation will never ask you to share these details.
Average loss: £3,011
5. Counterfeit or stolen goods
Either fake versions of branded or designer goods, or genuine items obtained through illegal means. The most common goods for scamming are furniture and kitchen utensils.
How it works Villains pretend to be reputable traders selling genuine items online or by knocking door-to-door. Counterfeit items may not meet the required safety standards and are usually of poor quality.
What to look out for: Be wary if the price is much cheaper than you'd expect. If it sounds too good to be true then it probably is. Someone selling items out of the back of a van.
Average loss: £165