i missed an appointment once
there was a massive gap in my diary, i had a small job in the morning and then this one at 5.30pm, i got carried away doing something and then forgot and went out with the kids i think. something like that.
i rang the next day and apologised, and i also offered to give them 50% off my original price to compensate, i've cleaned for them again since, at full price this time, phew!!!
ps.... i set my alarm on my phone now when i have a big gap like that one, problem solved.