NPR has done a couple series on how dollar stores (Dollar General/Dollar Tree/Family Dollar, just search "NPR dollar general" to see the content) can setup shop

NPR has done a couple series on how dollar stores (Dollar General/Dollar Tree/Family Dollar, just search "NPR dollar general" to see the content) can setup shop directly next door to a traditional grocery store and erode the traditional grocery store out of business. Reason being - dollar stores sell only the high margin items for low prices, whereas the grocery store has the expectation that they will provide all the staples people need, even the super low-margin items like lettuce. Once a grocery store loses the competition on the high margin items, they can no longer subsidize selling the low margin items and go out of business. A real (and growing) problem in many communities.