While you're right, you can feel cheated, it shouldn't mean that you need to nag someone about it. I've not read the books (though saying I was disappointed with the ending of the TV adaptation, is a massive understatement), but I've had other examples. All that should do is lose trust in that person, and potentially avoid their uncompleted other work, because the same thing might happen.

Taking your example, if my friend doesn't show up, assuming I don't buy his excuse, it means a) I lose trust in him when it comes to something that matter, and b) I'm less likely to ask him to help me move next time.