Third-party marketplaces are a growing force within retail. From department stores to grocers to big-box electronics and home-goods brands, many leading major retailers have launched a marketplace (or put doing so on their strategic priority list). Amazon popularized a model where the retailer does not control the product assortment and its selection and pricing, but instead third-party sellers—a mix of manufacturers, distributors, and resellers—own these decisions on the retailer’s platform.