The odd one, if they do it rarely and it's via text so I know before hand I let slide.
If it becomes a habit, more than twice a year without good reason (holiday, building work etc) I would probably get rid.
It does depend a bit in what stage of business you are at though, an irregular customer is better than no customer when starting out.
A doorstep cancellation is another matter though. If I'm being turned away on the door without good reason that's an instant dump. unless of course again there's building work or other good reason.
Just apply common sense