Now that I have my customers email addresses due to go cardless, i am going to send them an email stating that I am applying a £3 tip on their behalf onto the december clean. If they would rather not, then to contact me before their clean.
I doubt any would want to admit to being tight and therefore not contact me and I'm guessing the others wont even check their emails anyway. Or have them sent to spam. Either way, they cant deny that I sort permission first. Win win