You are right about supermarkets charging for shelf space in various ways, and to add to that I think it's even worse. I've heard the supermarkets and other retailer dub certain brands for certain products as "category leaders" and basically give them control of the entire shelf space of their category, including that brand's competitors. Which products and varities get stocked, how much, and placement. That brand is then in charge of maximizing profitability of "its" section. I'm not sure how that isnt an antitrust problem, but...