Extremely inconsiderate.
If you miss an oppointment with Dr Retherford without giving a 24 hour notice, you are charged a $25. This is reasonable, I have no problem with this.
However, Dr Retherford can and will cancel your appointment without giving you the same courtesy. I have a 4:45 appointment. I left work 2 hours early to make it there at 4:20. When I arrived, the receptionist told me my appointment was canceled. Apparently they left a message while I was driving over there, and she thought that was good enough. No apology or anything, just an attitude.
While Dr Retherford seemed like a competent dentist, I think you should choose one who will honor his appointments and not cancel at the last minute when he feels like closing early.