I need to be carefull with my answer with this or I will upset a lot of people..... What the heck I do anyway.
First, a lot of people think that qualifications are important - they are to a point to have a base but I have seen many who have masters degrees yet have no clue to real world training.
Don't get me wrong and think I'm saying that they are a waste of time... I have a ton of qualifications and letters to my name yet I never push that. What is more important is application of the knowledge and the results that they get.
One thing I look for is that if I see the trainer with the client on a machine then I know that they are not that good - they either don't know any better or just don't care - I'm sorry if this upsets some of the trainers out there but it's the truth but at least if you don't know any better then you can go out a learn but if you just don't care then you need a little more help.
I' a beleiver of attention to detail - that is the form in which the exercise is being performed - if the trainer allows the client to perform an exercise with poor form then that is not a trainer that you want.
I do at least 2 hours study 6 days a week and have done so for the past 20 years - I think this is somthing that is very important - I know that some trainers at California work crazy hours and don't have time for this but I do think this is more important - even if it's just an hour - or even better attend one of my seminars
I could go on and on but I hope that does help to answer the question a little - I hope other have some input here also.