With new ones i heard a good idea on here, that was to charge double on first clean and half price on 4th clean, that way your not getting messed about and they feel its a good deal... plus lets say it was a £10 house, if you just charged ten pound for first clean and all others that would be 40 but if you double the first and do half price on the 4th you still £5 up so its not a bad idea, but still the problem of losing time on the first cleans, but personally i would not be that bothered if i am gaining new work!!
Depends on a. how busy you already are, and b. how much you want the customer, i understand doubling it if its minging but if just dirty it doesnt always take twice as long!!