Joyce, Real Estate Commissions are always negotiable. That is the answer to the question as they teach it in Real Estate Schools. The true answer is that many companies do not really allow their agents to negotiate their commissions on their own, they must present their case to their broker for final approval.
The real answer is that costs across the board are pretty much the same for all brokers and agents, its only a matter of what services are provided for the money being spent. Some companies will charge less for less in service. Some offer premium services whether you need it or not.
If you wish to know what services the commission you are paying is getting you, then make a list and interview some agents. Most agents know that sellers seldom actually interview more than two agents. Interview agents and ask them what services they provide and what commissions they expect to receive for that level of service. Any agent is free to tell you they will not work for less than $"x" and that is their right. What is prohibited is negotiating commissions with the other brokers to keep rates higher. Costs are high, prices are low, sales volumes are also low, and agents do have the right to earn a living.