Not so fast. Just because a "teacher", if one prefers to call him that, doesn't have a TESOL doesn't mean he is "low quality".

"A TESOL does not a teacher make." --Rheno, ca. 2006 from the ancient ESOL scrolls

Nope, a TESOL means nothing. I've seen folks with nothing but bachelor's degrees (not in TESOL/TEFL) who were great. I've seen folks with all the bells and whistles that accompany a TESOL master's who were lousy.