There was a similar discussion to this a few months back and I was one of the many saying that I would go in heavy handed, pour dirty water through the letter box, knee cap them (Well, maybe not go that far!) etc etc!
But when I read how the experienced C/C's dealt with it, I completely changed the way I thought. There's usually a perfectly good explanation and 9 out of 10 times the customer will be a be very accommodating and certainly apologetic. It's usually an oversite which I am more than sure, every single one of us on here has been guilty of.