I can understand people running late .. I do run late from time to time, especially if I'm between jobs, or clients.
But, for me, it's always polite to either phone or send a text, to let them know.
My old farrier would run late, or early, and not tell me. Or he'd just simply not show up .. no call, no message.. I'd have to call him, and he would either be around the corner (after an hour of waiting), or "Oh yeah, I can't make it today, someone else needed me".
I gave him the flick ;)
My new trimmer is wonderful - we don't book a time, although she says 1pm, as she does the police horses before doing my 2, but I make it on a day where I don't work, and it's my 'chore' day (mucking out, riding, cleaning tack, etc..). She's usually on time at 1pm, but I tell her not to worry about being late - she's the most amazing trimmer, and I'm very lucky to have her do my horses. She is the ONLY exception to my 'being late' rule ;)
But as a rule, people, especially professionals, should call. People run late, horses play up, some take longer than others - I get it. But just let me know, so I can turn my horses out for a while .. standing for 2 hours tied up isn't fun for anyone :(