Price and Terms of Sale:
In most situations, the pricing of a property is determined by the input of three people or groups, the appraiser, the real estate agent (if their is one), and the seller. The appraiser is usually commissioned before a property goes on the market to determine the fair market value of the property, which typically determines the baseline for the price that the property will be sold at.
Depending on the property, there are other forms of appraisal as well; in commercial property, there are special appraisals called income capitalization appraisals, which generally determine not only the worth of the property, but also its potential to generate income over an extended period of time.
Multiple Listing Service:
A multiple listing service does not necessarily mean the same as a multiple agency listing (which rarely ever happen in the real estate industry due to the potential for a conflict of interest and the encouragement of unethical, competitive behavior between multiple agents or agencies). Multiple listing service is essentially as the name implies, a service that either allows listings from multiple sources or takes a listing from an owner (selling their property without representation) or an agency and places it under multiple listings. While they have always been around in some form, most commonly for apartment rentals or sales, the number of potential multiple listing services have exploded in the last ten years with the rise in prominence of the Internet in the real estate landscape.
Agency and Salesperson:
Most real estate agents or realtors, unless they specialize in high end real estate, rarely operate on their own, and can generally be found to be part of a larger organization, or real estate agency. The simple reason for this is financial. Most agents generally only make a few sales or purchases per year, and receive only a few thousand dollars on each sale after expenditures (not to mention taxes).
While in a very good year this could provide enough to live on, rarely does it provide enough for an individual agent to form the infrastructure and resources necessary to sustain a business (such as an office, or an assistant) Therefore, most agents find it economically feasible to be part of a larger agency, where they share part of their commission goes with the agency for maintenance of office space and other services, not to mention, ideally, profit.