In most places the basic requirements for entry level teaching positions are a degree plus a TESL/TEFL certificate - not necessarily a CELTA.

As with any job, the more you have to offer in terms of qualifications and experience, the better your chances of landing a well paid job with opportunities for advancement. However unless your intention is to remain within the ESL industry and build a career for yourself in this field then you could quite happily opt for a basic TESL/TEFL Certificate to add to your BA.

Being certified will make you more marketable and it will also prepare you for the job. Of course, if you are concerned about the validity of the certificate, then the only sure way to find out is to talk to the school(s) where you'd like to work. They will have their own preferences.

Hope this helps. If you need to know more email me anytime.