What's My House Worth?
The 'market value' is what a buyer would normally pay in a free market for your home, given no undue pressure to purchase.
It's not what you think your home is worth, or what your neighbors think it should be, or even what your mechanic thinks it should be. Buyer's are generally looking for a "good deal" - which is the most house for the least investment.
It's just like shopping at the store or the mall. You see a pair of pants that you really like, they're in your size and "Wow! They're on sale!"
As you pull them off the rack, you notice the sticker price. "Well, that's no sale price! I can get the same thing at XYZ Store for X dollars less!"
It's the same with houses. If you don't price your home at market value, the reaction of most buyer's will be the same as our shopping example. And for you, that's a big "No Sale". The big downside is if you leave your home on the market at too high a price, eventually you'll notice that no one is coming to view your home anymore. Word travels fast in real estate about overpriced properties.