I don't do it, because I don't ever go to Coles or Safeway anymore, but I now believe it is ethical to steal from them, where you can.
If they have an essential item, let's say veggies, which you need to survive with any level of life quality, and they are paying farmers the same as, or in some cases, less than they were a couple of years ago, while charging you more, then that difference is theft.
Because of the duopoly our capitalist dystopia has provided, some are now dependent on these stores for basic essentials. It's not an option for them to not pay the extra 25% mark up price gouge on a Zucchini, that serves no function other than to pad profit margins. That is theft. It is taking money from someone who has no choice in the matter, for no exchange of value or benefit.
So, as far as I'm concerned, you are justified in scanning your capsicums in as red onions. It's a mark down to offset the price gouge.