The Australian Competition and Consumer Commission has accused Coles of intentionally duping customers with its "down down" campaign, first launched in 2010.
In his closing submission to the Federal Court, Garry Rich SC argued the campaign was a tactic to deceive consumers that prices on thousands of products were falling, when in fact they were going up overall.
In one example cited by Mr Rich, the price of a jar of Coles-brand quince paste was raised to $4.50 from $3 for four weeks before being reduced to $3.15.
Mr Rich argued that four weeks was not a genuine establishment period for $4.50 - "price two" - to be legitimately considered the regular price of the product.
Justice Michael O'Bryan said he had to consider whether the "down down" price amounted to a genuine discount.
John Sheahan KC, for Coles, said the ACCC's case was flawed in that it relied on the amount of time a product was set at "price two" as the substantive issue.
"They treat what is an indicia, namely the period of time, as the substantive issue, when it is just an indicia," Mr Sheahan said.
"They have not advanced in their evidence a case that price two was not, in fact, a genuine price, except in the sense of it being relatively short in duration."
The retail giant has argued its "down down" prices were genuine discounts for shoppers after an increase in wholesale costs during a post-COVID inflation surge.
"Rising inflation is a matter of public commentary, it's a matter of political controversy and more to the point it's a matter of daily concern for shoppers," Mr Sheahan said.
Earlier, Mr Rich had told the court "down down" was not just a meaningless phrase.
"(Consumers) think it means something and what they think it means is that the price of this product has gone down," he said.
"They see a big red and white ticket and read that the price is 'down down' ... many of them will have no idea that the price was actually lower four weeks ago."
Justice O'Bryan queried whether time-poor consumers might take the meaning of "down down" to be simply a generic statement for prices as a whole.
But Mr Rich countered by saying "down down" immediately implied there used to be a higher price.
The commission alleges the supermarket giant deliberately raised prices on thousands of everyday items before offering discounts at prices higher or equal to the original shelf price throughout a period of 15 months.
The case continues.
