During my time in this business, I have a few times arrived at a customer's house either to find no one there, or to have the door opened by a customer who saw me, then said "Didn't you get my message that I had to postpone our appointment today?" Depending upon how far you have travelled to this location, this can be upsetting to you, and to your customer as well. If you use either voice mail or an answering service to take your messages, you should get into the habit of checking frequently to make sure that everyone you think is expecting you actually is awaiting your arrival.