Over here in Germany we have similar problems.
In my home town (~25.000) all the smaller food shops (we call them Aunt Emma Shops) vanished, only one still survived due to his special service delivering goods to the lot of pensioners who can't walk and carry. In 7 years the keeper will close because of old age, and he won't find a successor.
All butchers with joint pubs selling meals and self made cider have closed, too. Instead we have got a lot of new restaurants run by Italians, Chinese, Greeks, and Turks. They are mostly run by entire families: it's cheaper because no wages are paid to family members.
There are still bakeries and butcheries, some old, some newcomers.
We have a market twice a week at the main street since medieaval times where the peasants sell their products. The ware is a little bit more expensive than in the supermarket, but the products from the land are of a higher quality.
1. Landownership: The town has bought a lot of areas in better times; it is not obliged to sell to any possible buyer if the community doesn't like his plans.
Due to German laws the community has some very fine instruments to keep the big corporations at bay:
2. The plan for area use: Here the community decides what can be built in a certain area and what not (general rules)
3. The building plan: Corporations allowed to use a certain area can be stopped when the planned building doesn't fit the communities restrictions (special rules).
3. A resolution of restriction: Special goods and shops can be banned from the general rules of 2 when area development runs to the wrong direction (we did it sometimes when I was in town council to protect the shops in town centre).
In supermarket sector we have a monopolist in the country; we just got an interesting offer by another corporation for an area in my town. The monopolist is bidding against; who ever gets it will pay by buying the land for the next 3 planned social projects. I personally prefer the newcomer, due to an old proverb: competition makes business lively (especially for the customers, with lower prices.)

Wilfried