Two pages without a real response....might be a record.
What you're talking about is personal training and no there are no state sactioned or required liscenses like with physical therapy for example.
So as a personal trainer you are basically a salesman. Why should I buy from you when you have no certification or degree that shows you know what the heck you are talking about. Now, you might be the best trainer in the world, you might be very knowledgeable but people won't buy from you if you have no credentials.
What kind of training programs are you selling? Running? Weight lifting? Nutrition? You realize most of your clients will not be top line runners? Most will be 18-20 minute 5k guys in their 30s and 40s.
For distance running....get a USATF Level 1. That's pretty easy to get.
For weightlifting/nutrition you've got: ACSM-HFS, ACSM-PT, NSCA-CSCS, NSCA-PT, NASM, NASM-CES, NASM-PES, ISSA, ACE, and so on and so forth. I'd suggest ASCM-HFS or NSCA-CSCS BUT you need a health related degrees. 2nd tier option would be the NASM certs as you have a few options there and they were developed by a former NSCA guy.
Verdict: Spend $300 for the fitness cert. Spend another $125 for the USATF cert. Just because you are fast or in good shape doesn't mean people will listen to you or buy your product.
Alan