Hey Bull,
You can obtain your CFT ( Certified Fitness Trainer) certificate via the ISSA ( International SPorts Science Association). Im sure the Pros can share their experience.
You can go to their website and sign up for the CFT course. Its approx $550 USD and a package of the learning material and notes, practice tests are sent to you. They also host many seminars across the US to highlight some of the main topics prior to the exam. The exam can come in various formats but the best option is to the do the test after the seminar.
A CPR certificate is required prior to obtaining your certification. You can obtain this at any nearby Red Cross.
The contents of the course takes approximately 2-3 months of self study on topics such as Nutrition, Training, Anatomy and Exercise and Diseases. If you got background in Biology and have been training for a few years it does help tremendous. Nothing like background experience for this.
Dont let the CFT be your only qualification. Seek to gain further education in various facets of the sport and keep moving upwards.
Also, the course includes the business strategy and ways of developing that aspect of it, if you choose to pursue this as a career ( part time or fulltime) .
You can be a trainer for bodybuilding, the elderly, a sports team, young children, whether it be in a luxurious Condo Fitness Facility or private in house training, you call the shots.
Best of Luck.