Of the many requirements the number One requirement that you need to look in a trainer should be, Attitude.
Most times, clients pick their trainers based on the looks that he or she has. This is like picking a Cheese cake by its looks only to find later that the cake has rotten cheese hidden deep within.
If your trainer turns out to be just like the Cheese cake mentioned above, you are bound to end up either in the ER or discouraged and lost.
There are innumerable examples where Trainers behave as if they own their clients.