I can agree that nobody is perfect. And sometimes you get caught up in other crap. But if someone has paid you for goods, then it is YOUR job to let them know every single thing that is going on with those goods, imo. I just sent out a set of headlights.. guy paid me knowing I would ship them 2 days later. Those 2 days passed and something came up with my military duty and I was not able to ship until a week later. First thing I did was PM him and let him know the deal, and offer to send his money back to him until the end of the week when I could ship them.
It's never right to keep people waiting / guessing when they have already paid you.
Even on your phone, it takes just as much time to answer a PM as it does to post in a thread. There's no excuse for that when you could have simply PM'd them and let them know what was up with your situation.