Point is, it's easy to screech "predation" or whatever but the problem is that every one of these things has some justification that can be used in the abstract.
It does legitimately cost more to run a store like Dollar General than Walmart so the same can of beans has to cost more on their shelf for the same margin.
How much more, how much is justified? I don't know.
Yes, lots of businesses have thin margins. But the law (such as contract law and the laws against consumer fraud, which are implicated here) sets the things that a business can’t economize on in order to meet those margins. It’s the same as food safety: restaurants also run really thin margins, but they’re not allowed to store the meat on the counter because refrigeration is too expensive. If they do that, they get shut down by the health inspector.
Businesses “should” comply with consumer fraud laws for the same reason they “should” comply with health codes.