You can direct them to the Mobile Air Conditioning Society here.
Here is an excerpt from their Web site, www.macsw.org
"Section 609 of the United States Clean Air Act requiring all service technicians to be certified in proper refrigerant recovery and recycling has been law since 1990, yet many service professionals still are unaware of the requirements or have ignored them. Section 609 is a United States requirement and is not valid in other countries.
Many who have neglected this compliance are getting a rude awakening when inspectors from the EPA make a visit. MACS receives many panicked phone calls from service shops and fleets that need certification. Avoid a big fine by making sure all your technicians are Section 609 certified the cost is just $15."