When my older brother worked for a grocery store, salt was 10 cents a box. The manager frequently put it on "sale" 2 for a quarter. He sold much more salt during those "sales" that at the regular price.
Saw something similar in an Arkansas WalMart. Small bags of chips 25 cents each or three for a dollar. Had my wife read it to make sure I was seeig it correctly. I grabbed four bags and proceeded to check out where I told the young lady I would pass on the generous offer of 3 for a buck and gladly pay the .25 per bag. She looked confused!