There was a 17% increase in reported shopping scams during last year's Black Friday season, with victims losing an average of £538, a bank has warned in a report.
A survey for Barclays found more than half of Britons (59%) will change their usual behaviour while looking for good deals this festive season, with 38% planning to shop in the Black Friday sales around 26 November.
Almost a fifth of Black Friday shoppers (18%) said they felt under pressure last year to buy items as quickly as possible, and 14% said they would shop on unfamiliar websites if they had particularly good prices.
It comes as Action Fraud, the national reporting centre for fraud and cyber crime, said scam online shopping "bargains" that turned out to be too good to be true cost shoppers £15.4m over Christmas last year.
Last year the centre received reports relating to 28,049 shoppers conned out of their money while shopping online during Christmas, an increase of almost two-thirds (61%) compared to the previous year.
Pauline Smith, director of Action Fraud, said: "If you think you have found a bargain that is too good to be true, it probably is. Stop and think before making a purchase, as it could protect you and your money.
"Always shop with official retailers and follow our simple advice to enjoy shopping online safely and ensure you are not left empty-handed this Christmas."
Criminals took in £2.5m during the Black Friday and Cyber Monday sale events last year, an average loss of almost £550 per victim.
The Mortar Research survey for Barclays of 2,039 UK adults conducted in October revealed 12% of consumers would give their PIN to someone if they thought they were from their bank, and 25% would be likely to help if they were fraudulently asked to participate in an "internal bank investigation".
Some 43% of 31- to 40-year-olds said they would transfer money to a "safe" account if they thought their bank was asking them to.
And 35% of 31- to 40-year-olds and 23% of 21- to 30-year-olds said they would be likely to hand over remote access to their laptop or bank account to someone they believed was a bank employee.
Barclays head of digital safety, Ross Martin, said: "Whilst the Black Friday and Cyber Monday sales are a great opportunity for consumers to bag a bargain, unfortunately they create the perfect opportunity for fraudsters to target shoppers and it's important to remember that scammers often do target victims more than once and use details gathered in the first scam to strike again.
"If you receive a call from someone from your bank asking you to do any of these things, hang up and call back either on a trusted number or by dialling 159 - the fraud hotline. Please don't ignore your concerns - if you're ever unsure, always take the time to check."