Well using your example, I just notify the customer that if they expect the amp and projector to work they will need power. As a matter of professional courtesy I also inform sparky that he should expect a request from someone in the chain of command. He then has the option to be proactive or just wait till he is contacted. That is his business but at least he appreciates the heads up.

When game day comes the power is either there or not, what more can you do?