What is a Buyer?

A buyer is any person who contracts to acquire an asset in return for some form of consideration. When someone gets characterized by their role as buyer of certain assets, the term "buyer" gets new meaning:
A "merchandiser" or buyer is a person who purchases finished goods, typically for resale, for a firm, government, or organization. (A person who purchases material used to make goods is sometimes called a purchasing agent.)
In product management, buyer is the entity that decides to obtain the product.
A buyer's primary responsibility is obtaining the highest quality goods at the lowest cost. This usually requires research, writing requests for bids, proposals or quotes, and evaluation information received.

What is a Seller?

A ^seller ̄ or ^supplier ̄ is an company which focuses on moving products or goods through a supply chain network, domestic trade, or international trade. Suppliers can be any of the segments below:

Manufacturer - uses tools and labor to make things for sale
Processor (manufacturing) - converts a product from one form to another Packager (manufacturing), encloses products for distribution, storage, sale, and use
Distributor (business) - the middleman between the manufacturer and retailer
Wholesaler - sells goods or merchandise to retailers
Dealership - local franchised distribution
Merchant - a professional dealing with trade