Hundreds of customers of retail giant Currys have complained they were mis-sold extended warranties, a BBC Wales investigation has found.
In internal documents seen by consumer programme X-Ray, customers claim they were sold a warranty even though they said they did not want one.
Others say they were wrongly told they had to buy a warranty, the papers show.
Currys said the documents are a record of why people cancelled a warranty and do not prove mis-selling.
The firm said the papers reflect only a fraction of 1% of total sales.
Staff who have spoken to the BBC on condition of anonymity say they are under intense pressure to sell warranties - and other extras like in-store set-ups for computers or cables for televisions.
X-Ray asked one salesman if he had ever mis-sold a warranty.
He said: "I have had to on occasions to keep my job. I have a family to feed. I have to keep my job."
The internal documents seen by X-Ray document around 2,000 cases of potential mis-selling brought to the company's attention in a six-week period last year.
The report features incidents at stores across the UK.
In around 850 cases, customers said they were told - wrongly - that they had to take a warranty.
In another 1,250 cases they either refused a warranty, but were sold one anyway, or were sold a warranty without being told about it.
Prof Margaret Griffiths, a consumer law expert, said: "Companies are under an obligation to tell customers all the material information they need in order to make a proper informed decision.
"If a company has deliberately withheld material information then that would be contrary to regulations as it would be a material omission.
"That has the potential to be a criminal law offence."
Other documents seen by the programme show that staff can be put on what's known as a "capability programme" if they fail to sell enough extras, like cables, warranties and set-up services.
Some staff fear this could lead to them losing their jobs.
One whistleblower, who held senior positions in Currys stores over a number of years said: "The guy who is asking all them questions and trying to sell you the warranty and all the add ons - his job is at risk if he doesn't do it."
The company have strongly denied the allegations.
It said that the internal report given to X-Ray lists various legitimate reasons why customers cancelled their warranties and not just cases of potential mis-selling.
The firm said it uses this list to help staff identify issues with the sale of warranties and to address any problems with staff. And the claims of apparent mis-selling made by customers have not been proven.
Currys added that these warranty cancellations actually account for a fraction of 1% its their total sales.
The firm also stressed that staff are not rewarded for the inappropriate selling of warranties and add-ons.
X-Ray is broadcast on BBC One Wales at 19:30 GMT on 25 March. It is also available on the BBX-Ray iC iPlayer from 24 March.