The buyer of a property being sold in a short sale need to be aware of several key issues. The contract is usually contingent upon the agreement of the seller's mortgage lender to accept the net proceeds of the sale as full payment for the debt. This can, and is often, a long process. So, this could very well delay an anticipated settlement date. You will often know which homes are listed as short sales in the multiple listing services, either directly stated in the remarks, or have wording such as "requires third party approval".
I always like to recommend that if you are considering to purchase real estate, seek competent legal and financial professional help, or deal with a real estate professional with experience with short sale transactions.