Edd,
If they WANT someone's business it is considered a good practice to RESPOND to the customer. If not the customer will go elsewhere...... Maybe to another service, but maybe to ME. They might decide that "I was going to pay for a grocery stop etc, but if I can't get good service, I will pay Garden Grocer or ship stuff"
There's no excuse for NOT contacting the customer if you want to stay in business! Why should the customer have to make repeated attempts? There are lots of other options out there.....