I'd rather have a client arrive earlier, than late BUT I don't like being put under pressure to see them. One trick I've come across is client asks for a particular time, say 11am, I can't do that time but can see them at 1pm. They accept 1pm then on the day confirm asking for the 11am, when I can't do that they cancel.
Other examples have been someone asking for a time earlier than I'm prepared to start, agreeing a later time, then arriving at the earlier time - when I can't see them they cancel.