Workplace boundaries

I work with folks who work in vet medicine and it isn’t uncommon for clients to show up late for appts. or to bring 2 pets when they only had an appt for one. Like anyplace that schedules time for appointments this can throw off the entire day and cause stress amongst the staff and other clients who showed up on time for their appt. Are these not boundary violations? If so, in a customer service arena how do you enforce boundaries while risking angering someone or the real fear, they leave the practice all together?