I became ACE certified 2 years ago. I love fitness and I wanted to finally be able to help everyone who said "tell me what to do"....well I got certified and opened my own business as a trainer. I went to people houses and had folks come to my home gym. This all takes alot of start up money. You have to insure yourself, put a rider on your house in case someone gets hurt, pay the town you live in a fee for operating a business out of a home..and then you start with the all the paperwork stuff like waivers, business cards, client files...it's alot....but I do love it. I only do it part time because to be truthful people want to be trained early am and later afternoon, evenings. This leaves quite a few hours when your not making any money. For me it's not enough of a salary to support myself or my family,but it does add a few dollars to the household. I charge $50/hr and you have to remember tons of people cancel and quit! Even with no refund and late cancelation policies you still have quite a few people who get you to change your policy. There are alot of things to consider. I would think about why you want to do it and exactly how much money you need to make and then think it over carefully.
Hope this helps. Good luck!