No not at all just explain to them you dont collect and get all the first cleans done leaving your recipt with payment details on. after the 2nd, 3rd and 4th clean you will have some late payers from getting used to the change so maybe just collect those ones and when you see them face to face tell them that you dont collect, if you still cant get them to change then replace them and get rid(sell or dump them). Job done.