While it's true that the rules of marketing and advertising do still apply, there are also unique aspects.The main one being that wcing is loyalty based.Once you have a customer it's a good thing to hang on to them.WCING is a very small part of the customers overall world and whilst upselling is good, too much contact can lead them to dwelling on you too much.
The ones that phone you up a lot to say you are early,late,did a good job,etc, are also the ones most likely to cancel.A customer is a sleeping dog, let it lie.