Good food cost even less at Asda when shoppers paid what they thought it was worth when the supermarket's tills went offline.
Staff at Asda in Beddington Lane tried to come up with a solution after a power surge shut off all their tills for about two hours on Sunday.
Bemused shopper Joanne Waller of Wallington, said managers "ran around like headless chickens," before it was announced staff and customers would estimate how much each person's shopping came to.
She said: "It was so bizarre, the queues were all the way down the aisles. The checkout staff were literally holding up items and saying 'how much was this?' and then using pen and paper to write it down.
"Then the staff were trying to add it all up. At first they said it was cash only, but then they found a manual card reader; but they had to stop using it because it didn't have the Asda imprint on it."
Mrs Waller, 54, said while some shoppers abandoned their trolleys and left the store, others took advantage of the chaos.
She added: "The shop was absolutely heaving; it was a thieves paradise. People got bags from the self-service check-outs, took their trolleys around to a quiet area filled them up and walked out as though they had paid.
"I thought they would have been better of shutting the store and asking people to come back later."
A spokesman for Asda said there was no evidence stealing had taken place in store.
He said: "In these circumstances standard practice is to agree a price with customers already in store, so they can still take their shopping home and stock up their fridges and larders."