Commission rates

I am a new freelance trainer and am developing relationships with one or two training agencies. Can anyone tell me if there are standards for i)the % amount of commission payable to the agent and ii) for how long further work from the same client would be covered by the commission agreement.
Brett Robinson

I am a new freelance trainer and am developing relationships with one or two training agencies. Can anyone tell me if there are standards for i)the % amount of commission payable to the agent and ii) for how long further work from the same client would be covered by the commission agreement.
Brett Robinson