The model watches every customer for a few months and works out their personal booking cycle. Sarah comes every 6 weeks. Tom every 11. Megan whenever she fancies. Once it knows the rhythm, it knows what "late" looks like, for them.
Then it tracks the quiet things humans miss. Did they stop opening your texts? Did their messages get shorter? Did they cancel and not rebook? None of these matter on their own. But two or three together is your warning.
Every alert comes with reasons in plain English. "Eight weeks since last visit, usually six. Hasn't opened the last 3 emails." So when you pick up the phone, you know what to say. No guesswork.