The margin is an important factor in determining consumer prices, but it is not the only one. There are many reasons for selling a product other than the margin: assortment, increasing the basket value, promotions (e.g. gift products), bait products (which will make your customers buy other products with higher margins). The store's business policy and strategy determine the margin it wants to achieve on which product and the margin it wants to sell. Thus, it may also be justified to sell a low-margin product.