Good question, was on my mind too. The problem I could see is Walmart style - the predator will beat the prices of the non-predator down until the non-predator goes out of business, then raise their prices again.

They can do this because they are operating in other areas with predatory prices, giving them the ability to operate at a loss, and relying on the fact that at least some of those areas are not being challenged by non-predators.

Everybody seems to be playing the game right in this scenario. Interesting to try to come up with a good counter.

Does this actually happen? If a community opened up a co-op shop that started eating into the revenue of a dollar store, would the dollar store company try to fight back, or would they just exit that market?

Yes, I guess well capitalize companies could offer unrealistically low prices, but on the other hand, any kind of co-op or community driven organization has the benefit of not needing the margins. Dollar store investors are there to make a buck, if their capital isn't getting reasonable returns will ultimately exit the business and move somewhere else.