Currys PC World has apologised after customers complained they had been pressured into paying more than the advertised price for laptops on multiple occasions since 2015.
Which? said 108 customers had reported ordering laptops or seeing them advertised at a specific price only to be charged up to £40 more on collecting them.
Customers reported staff telling them that pre-setup computers were the only ones left in the shop, so they would have to pay a previously unmentioned additional set-up fee.
The retailer offers a £35 ‘Knowhow’ set-up service, as advertised on its website, which includes a USB recovery stick, but customers told Which? they were not advised it was optional.
The watchdog said it had raised the issue with Currys PC World “multiple times” since 2015, but continued to hear from customers with the same complaint.
The retailer said it was “urgently re-briefing” its stores to ensure customers should not be charged extra if there were only pre-setup models available.
All retailers are required to advertise the full price of a product that is bought online under the Consumer Contracts Regulations.
The retailer offers a £35 “Knowhow” set-up service. Customers told Which? they were not advised it was optional.
Under UK consumer contract law all retailers should advertise the full price of a product bought online.
A Currys PC World spokeswoman said: “We are sorry to hear that some customers have been charged for a Knowhow Laptop Set-up service on their new machine when they did not request it.
“While setting up machines in advance enables customers who want the service to benefit from it straight away, it is not something everyone needs.
“We are urgently re-briefing our stores now to remind them that, in the small number of cases where only pre-set up models are available, customers should not be charged for the service when they buy their laptop.
“We ask any customers affected by this to email us directly at whichsupportdixonscarphone.com so we can resolve this and feed back to our stores and regional managers.”
Which? said it raised similar concerns with Currys in January 2015 following a flurry of complaints on Reddit, and confirmed then that customers should not have to pay additional fees if they did not request the service.
It contacted the retailer about the same issue in December 2015 and March last year.
Alex Neill, Which? director of home and product services, said: “This issue has been going on for more than three years without resolution and we are disappointed people are continuing to report feeling pressurised into parting with their cash.
“We want Currys to make cast-iron guarantees that it will put an end to this practice and that customers who’ve been caught out will be reimbursed.”
In 2013, hundreds of Currys customers complained they had been mis-sold extended warranties.
Currys said at the time that documents seen by BBC Wales were a record of why people cancelled a warranty and did not prove mis-selling.