I bought a pack of beer a fortnight ago, and when I lifted the second can out of the pack, it felt very light. I shook it around a bit and it seemed to be about a quarter full. The can was unpunctured, its seal completely unbroken, so my beautiful and resourceful girlfriend called up their customer service line to mention it.
And they've sent her a letter and a padded envelope in which to return the faulty item for investigation....!