I will reschedule 1 missed appointment (stuff happens, I get it). The second time, I will not schedule them. They can drop in during my office hours and wait for me to have time to get to them. It usually ends up they mail or drop off or I never see them again. I really don't care by that point. If you don't value our time together, then I don't need you as a client. I know that sounds like I am being harsh, and I do need my clients, but if you stiff me twice, I lose respect for you and you get my very professional demeanor when you come in.
Tom
Modesto, CA