Percentages are individual, not even per brokerage; individual agents generally set their own rates. Realtors are independent contractors and run their own businesses.
Please do not shop by commission. A REaltor may charge a very large fee, but have such a well-developed marketing plan, that he/she is able to get a much higher sales price than an agent who may do no more than place the listing on the Multiple LIsting Service.
It is important to determine competency, experience, ability to negotiate, integrity and see a written marketing plan of what will be done besides listing on MLS.