The bank is the one who actually pays the commission in the short sale. The listing agent is the one who negotiates the commission for the transaction and then the commission is split 50/50 per standard practice in this area.
Short sales can be extremely time consuming and difficult and often agents get paid a pretty nominal amount compared to the amount of time, effort and negotiating skills needed to successfully navigate a short sale. There are many factors involved in successfully negotiating a short sale, and commission is only one part of it. Which bank(s) are involved, what are the terms of the contract that is accepted, how short is the seller, where there multiple offers, and other factors are looked at.
It might be good to find an agent that is familiar with the short sale process and has had success in getting all the information regarding the nature of the short sale to see how best to position an offer. You are hiring a Realtor for their professional knowledge and skills.
Keep in mind short sales can be a frustrating and often sticky situation. The nuances of a short sale change with every property, so having someone to advocate for you to the fullest extent of their abilities is extremely important. Potentially short changing their paycheck (and their livelihood) does not always best serve you.
Hope this helps!
Alain Pinel Realtors