Example: Seller bought property in 2005 for 500K. Now, the property is worth 270K, and the seller has been unemployed for the past 2 years, and no chance of employment. You, as buyer, offer 260K, the bank sends in a realtor to do a bpo (broker price opinion), the bpo comes in at 265K - you are in the ball park of the underlying investor, your short sale is approved. If bpo comes in at 280K, the bank may conter with the price higher than your offer of 260K.
Hope this helps,
Beachfront Realty, Inc.