Its usually just one of the steps to doing it professionally. Most states AFAIK also have a licensing regiment required to work on anything not covered by the s

Its usually just one of the steps to doing it professionally. Most states AFAIK also have a licensing regiment required to work on anything not covered by the small appliance 608 type 1 which covers more theory of operation code compliant installation/etc. So the EPA cert by itself isn't usually enough to work professionally (unless your repairing home refrigerators).