this happened to me years ago.
my customer was a single mum, a lovely young lass but too polite. The other cleaner was very hit n miss to when he showed up. The problem was though, that the streets he worked, all knew each other and he would always tell a different tale as to why hes not been for so long. So many got rid and came to me as I was reliable. (yes i did a good job etc, etc) but they knew I would be there every four weeks.
So I turn up to clean her house and make a start on the front windows (without the need to send a text, James 😉) and who should start walking round to the front from the rear, but this other chap. The young lass came to the door all embarrassed and paid him and he troddled off. I stayed n we got talking, basically she didn't have the heart to finish him, he charged £3.50 and I was charging £7 at that time.
I was polite about it but mentioned I would make it easier for her and stop coming.
lol, if they ain't got the heart to tell someone who came out possibly every 4 -6 months to clean the windows, to sling their hook. Then I ain't gonna save em by cleaning up their poor attempts at window cleaning.
likewise in your opening thread and especially if you have to take off/rinse off soap suds every time your cleaning. Then I would get rid of em as well