You can have terms and conditions to let potential clients know how you operate, when they need to pay, fees incured for late paying etc, etc, and they may well look verp professional, but in the real world they mean absolutely nothing.
Late payment fees?

?
If they're the sort of client who routinely pays up late I'm pretty certain you aint going to squeeze any extra out of them; they'll just cancel.
To be honest mate you'd be better off saving your paper as they're a waste of time; no matter what's on the paper, at the end of the day the client calls the shots. If they want you to clean that day fine, if not they'll just say " not today thanks " and there's bugger all you can do, assuming you want to keep them on your books.