I can't speak from your experience, but in my tech support days that worked a lot. I wouldn't ask people to blow on it though; my default excuse was technobable about capacitance build up, static charge, or occasionally blaming Windows.
Having people unplug/replug cables is a polite (if mildly dishonest) way to make sure the cable is actually plugged in. If you ask someone to check if a cable is unplugged or loose, they will often assure you it's not without ever checking. And you should check it when asked. A cable working itself loose over time happens surprisingly often. The world is an imperfect place; screws fall out all the time.