If at all possible, try to hire only degreed personal trainers. This way you are sure that they have all of the proper training to keep you safe from harm and offer you the best forms of treatment. Anybody can read an article or two online, take a weekend class and call themselves certified. They will not be able to provide you with the results you are looking for. A degreed trainer might cost a little more upfront in the long run, but they will get you to your goal. A certified (only) trainer will put you through a workout, but more than likely not one suited for your needs. You'll end up seeking out a degreed trainer in the end.