Typical gyms and studios' owners/fitness managers ears will perk when they hear that you are certified by:
A)C.S.C.S. (four year degree required to take test)
B)N.A.S.M. (correspondence study)
C)I.S.S.A. (correspondence study)
However, as eluded to by the other post, some gyms may desire another cert.
These are all BASIC, entry level courses that are popular with most people, so if you consider yourself a beginner (i.e. you have limited experience in either the health and fitness field and/or health and fitness in general), these are courses to consider.
With that said, there are other courses/informational sites to atleast pay attention to along the way:
A) Poliquin Performance Center (NOT for a beginner and NOT for someone who isn't financially secure)
B)C.H.E.K. Institute (holistic-based program that is definitely NOT for everyone...alot of dogmatic practitioner reside there, so beware)
C)ptonthenet.com (for nine bucks a month, it is an invaluable resource that has hundreds of differing opinions)
D)westonaprice.org (website dedicated to nutritional information)
Note: this list is obviously not inclusive, so research and ask others for more recommendations.
As for income, it all depends on the area that you'll be training, the gym/studio you'll be working at, your sales skill, your experience level, etc. etc. etc. It generally ranges from 25,000+ up to whatever you want to make...literally.
The business itself can vary considerably since each gym has its own identity. The chain clubs like 24 Hour Fitness and Bally's are usually a bad choice for most trainers-to-be, since the information that is taught to you is usually low grade and the wages and potential client loads are on the same level as a Wendy's employee. Smaller clubs and studios have alot of the same issues, but are usually more trainer friendly, since it's easier to get to know the gym members.
You will find that there is a disproportionate number of trainers that aren't making it, for whatever reason. In my opinion, this is because they went into the business without a defined plan. For example, if you want a full client load, you have to be willing to sacrifice alot of your free time in order to "prospect hunt." This is usually a hard pill for most to swallow since they have to spend free time making NO money. Another example is when ex-athletes get into the business and work in places that cater to non-athletes, women or the elderly...these are the wrong places for them to work. But the biggest problem I see with the majority of trainers-to-be is that they are lousy salesmen. To be completely honest...if you can't sell, you won't train. And it doesn't matter how much information you have floating around in the noggin, if you don't have paying clients...your knowledge will end up wasted.
If I could go back and tell my younger self a couple things before I started in the business, they would be to train people for free first and see how well you do, how much you actually enjoy it and see how well you to talk to and sell the average person. This way, if you find out that it's not for you...you don't have to sacrifice that much.
Some tidbits on the job:
*Most trainers will talk shit about every other trainer.
*Using information to sell clients does not work as well as using emotion...I hate it...it's a form of manipulation and I despise using this tactic, that's why I suck at selling clients.
*Corporate gyms are only interested in session sales and supplement sales...results are only slogans to them.
*If you decide to subcontract under someone else...GET EVERYTHING IN WRITING...EVERYTHING.
*If you're going to train the average person...get used to the idea of being a counselor or therapist.
*If you're going to train athletes...make sure that they hate the sight of you.
*Don't train people the same as you train yourself...this may seem obvious, but pay attention to how the majority of trainers do business and you'll soon find out that this is more of the case, than the exception.
*All women have lower abdominal issues...the one's you're likely to begin training that is.
*Nutrition is the foundation of life...don't neglect it, don't marginalize it and don't let them tell you that they thier diet is okay...if it were, they wouldn't need you.
*Success is a relative term...if you only have two regular clients who have reached every goal that has been set, you are a far better trainer than the guys with full client loads and every client looks like a weight watcher member.
*If you don't believe in people...don't become a personal trainer.
I hope some of this helps...if you have anymore questions or concerns ask other trainers on this site, in your area, on other websites so you can get a broader picture. I am only one perception so my thoughts should be read in this context.