Their reported profit margins are also super suspicious, TBH.

Because the grocery chains have subsidiaries that are almost always the owner of the real estate where the stores are located. So they can just set the rent cost of the store in order to get whatever profit margin they deem acceptable.

Then the real estate subsidiary turns around and spends most of their profits buying more real estate. You see it almost everywhere now, grocery subsidiaries buying up whole blocks of nice hhouses, just to demolish them and build ugly concrete cubes with yet another grocery store on ground level and stacks of tiny apartments on top.

The best thing that can be said about these buildings, is that hopefully teachers in a few decades can use them as clear examples to show children just how bad it gets when we let rent seeking MBA fuckers decide things.

Good question. I worked for one of them around 2005, and my boss mentioned price scouts then. As I recall it he wasn't happy about them, equating it with cheating.

The allegations are that the price collusion really took off around 2010. We had had a few foreign companies trying to take hold, like ICA in 2003 and Lidl in 2004. Lidl faced a unified publicity attack by the big three, and didn't last long. ICA bought one of the then-larger chains, but couldn't make it work and gave up in 2015.

It wouldn't surprise me if the "big three" started working more closely together during the "Lidl invasion", and that that laid the foundations for further cooperation later.