Project management must be aware of who the seller is during any project. The seller will either offer materials or services to management, or those working on a project might be looking toward the goal of being the seller of the end result. A seller could also be offering a service. Contractors are sellers project management might employ for their services. The contract workers are selling their expertise.
Most often, the seller is thought to be the retailer who sells the final product to the public, but project management also acts as a seller when the job is completed since the finished result will be sold to another party who might sell it to another. Sellers reside in all steps of the business ladder, and buyers often become sellers themselves when they put wares they bought up for resell. The farther down the line from the initial manufacturer, the higher the price the seller is able to charge. This is since every time a product or service is sold, the price is increased to make up for the cost of those from whom it was previously bought. Project management needs to be aware of this price increase if seeking to purchase supplies for a project.
This term is defined in the 3rd and the 4th edition of the PMBOK.