I noticed that this question was asked about a long time ago, but we want to contribute for anyone else that comes across this thread.
Commission is always negotiable, and the Department of Justice even condones it as good competitive behavior among agents. The seller does pay the commission that covers both agents. But in a way, the buyers also pay for it since commission rates are typically accounted for in the selling price.
Many agents are willing to be flexible on commission rates, but it's not something they like to advertise. And most clients are not very capable or comfortable negotiating rates.
At UpNest (http://www.upnest.com), we created an online marketplace where home sellers can confidentially submit their homes, and multiple top local agents will compete to obtain your listing. Some agents lower their commission rates to stand out, and every agent that submits a proposal is an experienced agent, so it's not the same as working with a low grade discount brokerage.
Hope that helps!