The main qualification is that you are in some type of "financial hardship". This can include: loss of employment or income, divorce or separation, relocation or job transfer, major illness and medical expenses, or high dollar repairs without the resources to make them, or increased bills or living expenses. A good rule of thumb is that a short sale is not for those that "want" to sell, but only for those that "have" to sell. You typically must prove your inability to pay, however many lenders have become more lenient lately and will make acceptations sometimes for homeowners who are not even in hardship.
As a Realtor I will talk with you and help you to understand the options you have, so you can make a decision on which option is best for you.