Marshals should lead by example and post their route/distance choice and Speed groups online ahead of time.
Since the ride starts can be chaotic, as marshals we need to take charge and state our intentions and help other riders make a decision more readily. If the choices are clear at the start of a ride, it then becomes the responsibility of the individual to have chosen the correct route/pace group and therefore absolves any recourse. With that said, sometimes people make mistakes and try to bite off more than they can chew.