Your trainer may sometimes be absent because he has an emergency to attend to. This does not mean you should stop your workouts. The trainer should be able to explain things to you on the phone as well as teach you how to perform certain moves without being present.
You do not want a trainer that is impatient and easily gets annoyed or angry when you are not going at their pace. They should find an agreeable pace for their trainees. This is important because what works for one person may not work for another.
There should be certain boundaries your personal trainer should not cross even though you do not mind having a close relationship with them. This is why they should be professional and part of being professional is knowing these boundaries and respecting them.
To get the best out your exercise and training sessions, you must hire an experienced instructor. The trainer should not be an amateur or learner because they must understand the techniques and demands of aerobics.
As a client, you want to ensure that instructor has your best interest anytime, any day. The trainer should not be abusive or bad mouth you when you are not with them.