I know there are costs, but what I m saying is that these prices are exceeding what it cost. I put the example of Dia, a smaller chain that puts products at half of what it cost in Carrefour. It is also a chain and has -more or less- the same cost than them.Sounds like more monopolies in the food chain, if only we had a govt who cared about that sort of thing.....
Don't get me wrong, I really don't like supermarkets but for cleaning stuff, household produce etc, it's the cheapest and simplest for me. I try not to get too much "real" food from them. Discount days are hard to ignore however.
That said, you're economics are way out and you keep ignoring the mention of all the costs they have. It's killing me to defend them, especially here where as you correctly mention monopolies in the food chain are an issue, primarily with quality, but it would be ignorant (in the most repectful way) not to acknowledge the cost of operating a supermarket.
Here's a fun exercise, are there balance sheets and fundamentals of these companies not available online? With some research we could probably talk real figures and see what the year on year increase in profit really is. Guarantee you'd be surprised.