You can see people or signs marketing their home stating they are below market value or below appraised value and think that will make the home sell. They will also disclose that if the home is sold using a realtor the price of the home will be increased. This increased price will cover the costs of professional commissions. As a seller this can backfire and would encourage you to market your home at the best value that would include professional fees, just like when you go to the doctor.
Market value is determined by what a buyer will pay for something and what is the best price a seller can get for what they are selling. This is the exact same concept that is used with the stock market. At this time we are in a buyers market and buyers are determining much of the prices. This is also cyclical as it will swing back to a sellers market in the future... and again back to a buyers market over time.
Many real estate professionals will not take on the responsibility of listing a home if they believe it is above market value or over priced. There are some agents that will take on a listing based on what the homeowner dictates regardless of their knowledge of the area. In these cases this increases the inventory of homes in the area as well as the amount of time a home will remain for sale. Homes will sell if priced right and marketed correctly.
A professional realtor can help provide guidance as to a price range that your home may sell. And when buying they can provide assistance with what the homes in the area of your search or being offered at, amenities and what has sold.
Know before you buy or sell... and you will be able to get the best value for your home on either side of the closing table.