If you get a job with a chain they will probably certify you or maybe put you to work right away.
I don't think most teachers have much, if any, certification. Most students will just look at their dancing and competition results and then deterimine if they would be a good teacher. If one is a seasoned competitor--still competing-- with results and is still taking lessons themselves from high level established pros--this is a good indicator.
Dance Vision has some type of certification programs for teachers.
If you start out as an independent and rent space--a few students is all you need. How do you find them? By demonstrating your dancing skills at social events, doing exhibitions, or competitions. Getting students is more about marketing. Keeping students requires results and having a good teaching style. Many dance teachers keep their day jobs and teach part-time.
Teaching Int. Latin is very specialized and requires a serious commitment from students. Int. Latin is not really social dancing--it takes up more space, the technique is very detailed and not easy to learn.
I have never asked a teacher for any type of certification. I want to see them dance with a partner, look up their lifetime competition results on dancesport, and listen to they way they talk and express themselves.
Contact the organization from which you wish to receive certification. Most of the reputable ones will not simply test you, they require you to do have an endorsement to take the exam from someone who trains future teachers.