Unless you have special skills or a college degree you are low on the list of qualified applicants.
Also, your background needs to be really clean with a stable history.
On another note, and I do not mean to be harsh, but you mentioned you failed the POST entrance exam twice. In the academy. the LD's and academic testing, not to mention the writing you will have to do, is about 20 times harder. That POST entrance exam is the minimum level to move forward into the academy.
I might recommend that you get an AA degree in Police/Criminal Science first, maybe a sociology degree to get some kind of credibility. Also, volunteer some time somewhere to show how you are vesting yourself in the community. Personally I would recommend getting a BA/BS degree in something you like first. Maybe volunteer at your local PD
At the last SBCSO PT test about 2500 people showed up. So if you pass that test, what sets you above all of these people when you go to the interview/background process?
Agencies are looking at the whole picture that is "you", that POST RBC cert is just a small part of that picture. It just means you met the minimum education/testing requirements to enter into the next phase of law enforcement.
My last question is how successful will you be on getting hired by a department with a P.O.S.T certificate at this current time? I know a few departments are hiring like Pomona and Riverside. I failed both P.O.S.T. written exams and have a waiting period of about 3 to 6 months to take the next ones. I figured during this time I would just sponsor my self to keep ahead of everyone else. Seeing as the next classes will start in a month or so.