Students should not be overly upset at being 'stood up' occasionally. Professors really can be absent-minded, and plans do change. Keep making appointments. In our experience, students are prime offenders in this regard, no-showing or being very late as much as a third of the time. Try not to forget your appointments.
All advisors are very busy.
However advising is an important part of their job, and one they should take seriously. Some of our very best advisors are our very busiest. What is important is not how busy an advisor is, but what priority he or she gives to students. Occasionally an advisor will be out of town, or too busy to see advisees. But an advisor should make time, usually within a week, to see an advisee.