There are many aspects you should try to find out. You should find out about qualifications, experience and the trainer’s philosophy. Also important is the area of specialization and expertise so that you can figure out if the fitness professional can actually be a good match in regards to helping you achieve your specific health & fitness goals (post-rehab, sports conditioning, etc).
I see that you are a studio owner and personal trainer yourself, and I assume you want to know what traits potential clients are looking for in a personal trainer.
Here is what I tell people who ask me what they should look for in a personal trainer:
Ask about qualifications and experience and see if you can talk to a current or previous client of the trainer who may be similar in requirements to your own. For example, if you have back problems, make sure the trainer actually has practical experience rather than just theoretical one.
If the trainer is willing to train you right off the bat without any assessment, run the other way! Those famous “free personal training sessions” can come at a high price. Make sure the trainer listens to you and takes notes. You should have her full atttention. A trainer should be able to explain why he picked each exercise and modality.
In addition to the above posts, I’d like to add:
Personality. It should mesh well with yours, and given a good connection and communication it will keep you (perspective new client) coming back.
A good listener. The trainer should hear all your concerns and address them appropriately.
A coach and motivator. They should be in your corner, training you with your best intentions (and SAFETY) in mind, always.
From a client perspective, what I think are some of the most important qualities (in no particular order) are: good communication (both speaking and listening), technical knowledge in the field, enthusiasm for what they do, being a good role model, being organized, professionalism (which can cover a whole laundry list of other traits such as being “present and in the moment” with their client – i.e. not distracted), being a good ambassador/role model for health and fitness, and being empathetic.
Our jobs as personal trainers are immensely important in that the client is placing a lot of trust and faith in us by turning a good deal of their health and safety over to us. We need to respect the role that we have been placed in by doing the very best we can for EACH client we see.