Rockefeller set prices low to run others out of business. Just showing that it works both ways, and setting low prices is the common way to run competition out of business. You don't raise prices if you seek to close some doors or make them ripe for takeover. You peg the price lower.
Governments use price supports, but that goes to an entire industry such as dairy farmers to support the price of milk to make sure there is a supply. Running stores is entirely different.