I went to a place where the creditialed trainer kept pushing me to do a cardio workout way above my ability. It took me a couple days to recover. He did a bootcamp workout with me. When the credentialed trainer I was working with at home heard about that workout she was appalled. Some are better than others. The credentials don't mean a whole lot - it's a day or two of testing at most depending on which organization they go to for certification.