As of January 1, 2018 the EPA added new regulations in regards to the purchase of refrigerant. See the EPA website to read firsthand the changes and requirements.
https://www.epa.gov/section608/refrigerant-sales-restriction
For Large Cylinders – over 10 pounds – the seller must keep an invoice listing the name, date, and quantity of refrigerant sold. The seller must see a section 608 or 609 technician certification card. If the purchaser is acquiring the product on behalf of a shop, then evidence must be provided that at least one of the technicians in that shop is certified. The seller must keep a copy of the purchaser’s technical certificate on file and all records must be kept for a minimum of three years.
For Small Cans – to the general public, two pounds or less of R134a – There is no restriction on sale of cans less than two pounds, but the can should be manufactured with self-sealing valve.
For technicians who have completed section 608 or 609 certifications, the certification does not expire. For technicians who have misplaced their credentials and require a new copy, please contact the issuing company (eg: MACS) for a replacement. A processing fee may apply. For technicians who require certification, please visit the MACS website (www.macsw.org) for section 609 certification including training on handling the new refrigerant R-1234yf. The training and certification test cost $20.00.
Iceman Cooling Journal 