Do you feel comfortable around them or an “affinity” of some sorts? You will quickly find out that sometimes you will need your trainer to act like your fitness therapist. No matter how great the coach may be, if you don’t feel a level of comfort with them, you won’t be able to open yourself up to be helped.
If you do decide that a trainer is right for you, realize that you’re unlikely to have the same one for life. You’ll outgrow some, find others that can teach you something new, or decide to train on your own either temporarily or the rest of your life. Compatibility is a fluid thing. But if they do their job, you will outgrow them, because you will be far different than your future self.