Your job is to keep everyone else honest and to keep them communicating.
At the end you will be asked to give a short summary of what occurred
in your team. Focus on what went well and what foul-ups happened.
Did the developers build what was wanted?
Were the customers happy?
Was everyone honest?
Were deadlines met?
The main rules that you must enforce are:
(1) The developers estimate time, not the customers. The developers also specify
how much of the full development cycle they will be able to effectively deliver.
Make sure that the customers keep the total to this limit.
(2) The customers specify features, not the developers. The developers shouldn't
anticipate future needs or otherwise draw what is not asked for.
(3) The developers draw, not the customers. Don't even let the customers sketch.
Don't let anyone try to intimidate anyone else.
Keep everyone communicating. Make sure the customers and developers treat
this as a "full information" exercise.
One of you should also have a watch with a second hand so that you can
periodically announce the remaining time in the current cycle. The first story
writing cycle is 10 minutes and after that the development cycles are 10 minutes
and the interspersed planning cycles are 5 minutes starting with a planning
The customers are the final judge of what they WANT, but you are the final judge of what they SAY they want. These may differ of course. Therefore, the developers may do what is asked for, but not what is wanted and things will need to be respecified in the next cycle.