Being the world’s largest retailer, Walmart has vast bargaining power over its suppliers. Many suppliers are heavily reliant on Walmart’s distribution and will exchange lower prices for the higher volume.
To keep costs down, Trader Joe’s buys directly from suppliers whenever possible, they purchase items at high volume, products that aren’t selling are quickly pulled from shelves to make room for other things, and they stock their shelves.
Amazon Fresh stores take grocery store technology to a whole new level. Shoppers use dash carts, shopping carts with a touchscreen, barcode scanner, cameras, and various sensors to count items placed and removed from the cart automatically.