i think that if you're working a bank holliday for normal rates u should state a reason to the customer as to why you're bending over backwards, otherwise they learn to think you're some kind of lunatic that likes to give everything away for nothing and will come running any time of the day or night that they may throw you the odd titbit.
i used to do it, but nowadays i try to build value into my services. if i put myself out for someone then i tell them, it's because i want the other 60 odd properties you need cleaning as well, do you have a problem with that mr customer?
regards
Dave