What's Tefl.com selling?
It is an advertising center for those sorts of courses.
Here's the story they're telling on their website:
"Gone are the days when any native English speaker seeking a life of travel and adventure could pursue a successful career as a Teacher of English as a Foreign/Second Language without experience or qualifications. Almost all employers now seek teachers with a TEFL/TESL qualification plus experience, in addition to a first degree. Many even insist on an MA Linguistics/TEFL/TESL postgraduate qualification."