IN a dual agency situation, a lender on a short sale will typically reduce the commission. The market average these days seems to be 5% (2.5% each) when the listing and selling agent are different. When the listing agent represents both, the lender typically only pays them 4%.
The big advantage to using the listing agent is that they have control. More often than not, al ender only wants to review one offer at a time. Usually the buyer for that offer is long gone by the time the approval comes through. With an approved price, the listing agent can select which offer gets submitted next.