I can remember rumours in the 1970s that two grades of electronic goods were made - one for the shops and one for warehouses like Comet. There was even a variant on the rumour that the 'shop' models were tested and the ones for Comet etc were untested, meaning that equipment bought in Comet had a higher failure rate.
Another rumour was that Comet had heated storage areas and Dixons were unheated therefore equipment bought at Comet would be more reliable.
I assume all urban myth?