Tips on choosing a personal trainer?

Time for me to loose a good 50lbs. Dont know what to look for within a fitness trainer.Tips on choosing a personal trainer?
I used to work as a personal trainer and I would say what you want is someone who will consistently likely to push you to do a little more (about 15-20% more: five more minutes, two extra reps) than what you would do yourself.-> Not profusely more, if working out feels close to torture it is difficult for you to make it a consistent need.
He or she should lay out a program for you that includes cardio, flexibility, free weights and machines.
He or she should be very sensitive also to any preexisting injuries or robustness conditions that you may have, and should help yourself to time to instruct you on the proper form so as to protect your joints (i.e., not going too gaping in the bench press, have your feet far ample forward in the leg press, etc.)
You can also check to see through which group they are ascribed, one good one is ACE, ask them if their documents involved in-person instruction and evaluation or if it was solely self-study (aka correspondence course) the former is unmistakably more desireable, some trainers hold bachellor's degrees within exercise science or physiology.
Get someone NSCA-PT certified. This is the best (or one of the 2 best) certification for personal trainers.