You have choices when it comes to a short sale.

For many a short sale is a last ditch effort to salvage their credit rating.  Since so much hinges on the outcome of a short sale, home owners need to make a wise, and informed decision.

One of these choices is, which Real Estate Broker is going to sell the home, and which Agent are they going to use to represent them.  Is the Agent marketing the home like it is their own?  Does the Agent market the best features of the home?  Are the number of pictures adequate to show these features, and of a high enough quality to attract interest from all potential Buyers?  Does the description peak Buyers interest, or does it leave unanswered questions?  Is the home owner satisfied with the effort and details of the marketing plan? 

These facts should be reviewed before signing a Listing Contract.  This contract should also contain the following contingency. 

Seller may cancel this Agreement prior to the ending date of the listing period without advance notice to the broker, and without payment of a commission or any other consideration, if the property is conveyed to the mortgage insurer or the mortgage holder.  Sale of the property is contingent on written agreement to all sale terms by the mortgage holder and the mortgage insurer (if applicable).
Http://www.hud.gov/offices/adm/hudclips/forms/files/90045.pdf

In many cases the Listing Contract will be valid until the property either sells, or is foreclosed.  It may be very difficult to void a Listing Contract and change Brokers.  You will have to consult an Attorney if you wish to alter, or terminate a Listing Contract without the consent of the Broker.  This is why homeowners facing a short sale must be very careful in choosing a Broker and Agent. 

Make certain everything is in writing.  If you feel a need to have a written marking plan before signing a Listing Contract, you have the right to make it part of the contract.  The contract is an agreement between you and the Listing Broker, it should be a comfortable arrangement for the two of you.