Currys PC World has apologised after it was unveiled that customers were "pressured" into paying an optional £35 set-up fee for a laptop.
Consumer group Which? claimed that more than 100 customers had reported being given no choice but to pay the extra amount when they collected their laptop from the retailer.
Staff apparently told customers that the only computers left in stock are ones that had already been set up with its "Knowhow" service, meaning they would have to pay a previously unmentioned set-up fee.
The retailer's Knowhow set-up service costs £35 and customers told Which? they were not advised it was optional.
Which? claimed it had raised the issue with Currys PC World "multiple times" since 2015, but complaints have continued from customers since.
"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," said a Currys PC World spokeswoman.
"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 rebriefing 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."
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 that 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 have been caught out will be reimbursed."
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