Short Sale is a buzz word that should not be taken lightly.
Short sales must / should be approved by the lender first. Choosing to sell short without the lender approval is not good representation by the Agent.
Even with the short sale addendum, signed by the seller, consulting the lender for approvial before listing that home as a short sale.
The other aspect of the short sale, does the seller have the money to bring to settlement to make up the difference of what the home sold for and the balance of the mortgage ? YES, then should not be a problem. NO, will there is the challange
When the seller does not have the money to make up the difference in the sale price and the mortgage balance, that "short sales" MAY have financial and credit repercussions for the seller too. Consult your tax adviser.
Just walking away because your home is worth less then what you paid for the home, is not a good idea. Most Loan / Mortgage companies have departments and personal to help that seller. Call the Loan company or yoru title company for options FIRST.