The scams most likely to catch customers out have been revealed by NatWest as it works to raise awareness of the common tricks used by fraudsters.
The bank said its records show nearly 7,000 customers have become the victims of scams since the start of 2016.
Among these cases, "goods not received" cases - when someone pays for items or services that never turn up - were the most common.
These account for 2,073 cases seen by NatWest - or around three in 10 scams carried out against NatWest customers.
Such scams can happen on online auctions and marketplaces, NatWest said.
It said customers can protect themselves by checking the item description carefully and reading the website's dispute resolution policy before buying.
Customers should also use recognised, official payment services and not pay via direct bank transfer off-site, the bank said.
Business customers can also be victims of scams. NatWest said "invoice fraud" can cause particularly big losses. Invoice fraud happens when a business receives an invoice that appears to be from a trusted trading partner but is actually fake.
The fraudster typically says that payment arrangements have changed and that the customer should pay the outstanding balance to the new account, which is operated by the fraudster. Each business targeted loses, on average, £30,000 to this type of fraud.
The findings were released as NatWest was holding an event in Westminster to highlight fraud. The company is supporting an initiative from National Trading Standard called Friends Against Scams.
Les Matheson, NatWest chief executive of personal and business banking, said: "We know scammers can be convincing and they work round the clock to persuade their victims to part with money.
"We have hundreds of people working 24/7 to detect and stop fraud, but it's very important that, as individuals and businesses, we know how to protect ourselves."
Here are the top five scams affecting NatWest customers and an explanation of them:
1. Goods not received - You pay for goods or services but do not receive them from the seller.
2. Advance fee fraud - Fraudsters ask you for an advance or up-front payments for goods, services and/or financial gains that do not materialise.
3. Spoof payment requests - You receive a fraudulent request, purporting to be from someone senior in a company or a client, for payment or draw down of funds.
4. Invoice fraud - You are tricked into believing an invoice is from a trusted trading partner when it is not. The fraudster will tell you their payment information has changed and you should pay the new account.
5. Holiday scam - You book a holiday, usually online, to find out later that the holiday is not real.