芳，这都不知道啊？经济风暴都白风暴啦：））

short sale 就是市场价低于欠的钱， so when you sale the house, the sale proceeds is "short" of martgage balanceand , and the bank have to take a loss, if short sale is not successful, the house typically goes to forclosure.

The appraised value for tax purpose can be very different from market price because all the houses in a town have to be valued based on a particular time point, or newer house has to pay lots of more property taxes(if the house value has been raising). 20% is not very high actually, my old house was sold 3 times of appraised value (for tax purpose).