There are other options. If the government operated a store where there were guaranteed prices on certain goods and they were available in sufficient quantities, it would effectively peg the price of those goods in the rest of the market as well. This could be a cooperative or something similar.
If the market isn’t performing its function then that is when the government needs to step in and change the rules.
In this case our grocers aren’t competing on price enough, so they’d be adding more.
There are other options. If the government operated a store where there were guaranteed prices on certain goods and they were available in sufficient quantities, it would effectively peg the price of those goods in the rest of the market as well. This could be a cooperative or something similar.