Like a real estate market in its infancy, domain names are an important commodity for a business. Many times businesses will attempt to register a domain and discover that the domain they desire is already registered.
This does not necessarily mean that the domain is in use. Some domains are registered in preparation for the start of a company or remain registered after a company closes. These domain properties are often bought and sold through an exchange. A prospective buyer can search through the exchange looking for keywords or categories or other unique identifiers that will create the potential for a successful website.
DealASite.com is an exchange that offers a place for sellers to list sites and buyers to place bids on sites. It works kind of like a lendingtree model.
A seller lists a site, and may or may not put a minimum price on it.
Prospective buyers can then bid any amount above or below the minimum.
When the offering period expires the seller then has the option to sell the site to any of the prospective buyers regardless of the bid amount or the seller can hold the site and not sell at all.
Dealasite leaves the financial transaction up to the two parties, but does recommend the use of Escrow.com to help insure that neither party is defrauded.
Some live websites are even offered up for sale as a fully functioning business that can be purchased and taken over just as any performing business asset might be purchased.
Like a stock or commodities market, some buyers will even buy and sell domains on a regular basis looking for undervalued properties and turning them at a profit. Like a residential home improvement flip scenario, some web designers will purchase an existing functional website, work to improve the site, its traffic and revenue and then flip the business property to another buyer later.