Just last week we had an old lady and her daughter (30ish years old, now) come in: daughter had bought a clock-radio cordless telephone (I work at Dick Smith Electronics) for her mum, who claims the LCD didn't work properly: it looked like it was showing all the wrong numbers. The daughter confirmed it -- she had taken a good look at it, and couldn't work it out either. They offered to show me, but I told them if they brought it in, there's probably something wrong with it, so I trust them and I'd just swap the unit.
So, I go grab the new one, and they ask to test it to make sure it's not another dud. Sure, no problem. We go over to the other side of the store, and unpack the box (You need a uni degree in box-packing to get these things back together, so unpacking it is a big deal) and plug it in.
So, the LCD lights up fine -- numbers displaying. I showed it to them, and they said "no, no, this one's got the same problem, too! See? The numbers all look funny!"
....the plastic LCD protector, that's put on any LCD (ie on mobile phones, too) was still on the unit, and had "12:00" printed on it to demonstrate what the LCD should look like. Upon inspecting their 'faulty' model, they'd never taken it off either: 2 seconds later their model was good as gold. Needless to say I had to get the replacement unit back into the damned box...