1) You should know that they have processed many short sales before.
2) That they are proficient at handling the bank, or have representation to do that.
3) They should ask the questions of what type of loan it is, FHA, VA or conventional, who the loan is with and if there is more than one loan.
4) They find out if you qualify as primary home, 2nd home or investment and be able to tell you what each would do for you.
5) They have taken courses educating them on short sales.
Basically, you need a good Realtor who will push to get these files through, as a passive realtor will not work well for you.
I am an experienced short sale realtor and would love to assist you if you have not already chosen.
Regards and Happy Thanksgiving,