When a customer makes an appointment with an email, first name and last name must exactly be the same as entered on the previous appointment. But it seems to be case sensitive, e.g. "John" is seen as differnt from "john" and even leading or trailing spaces make a difference, e.g. "John" is different from "John ". This obviously leads to a lot of confusion for customers. Is there a setting to make names case insensitive, and to trim spaces?

I can't imagine john doe, John Doe and John Doe  (notice the trailing space) being three different customers. I have no idea why you'd spoil your nicely designed UI/UX by making case insensitive names and trimming spaces an option; I would do this by default. 

People often type their name lowercase on mobile devices, and trailing spaces are a common side-effect of copy pasting it from somewhere else.