I guess so, but in truth it doesn't work like that, you dont save the money you just save the couple of minutes to take you to knock there door and say that x amount please. Bt the time saved could be ofset by the time you spend checking that payments have went through, and if one cancles there, you are still going to have to send out invoices.
I dont know how it would work but, if they do pay by dirrect debit does it come up there name, I mean how do you know what customer it is for, and even if it comes up mr dochery tranfered x amount, I have about 20 docherty's how do you know which one it is.
Also as someone mentioned, I work 4 weekly not monthly and dd come of a certain day of the month.