When I'm looking for teaching jobs in Korea, I can ask my price as long as it's within reason, and I know what I'm worth to prospective employers. I also know that a TESOL (Teaching English to Speakers of Other Languages) makes me more valuable, and thus able to ask a higher salary. Thus, while I was in Korea, I used the abundance of down time during exams week to get certified.
The process of gaining certification also made me a better teacher, helping me in classroom management and in engaging the students.
Here are my certificate, transcript, and letter of recommendation from ICAL: