Good Agricultural Practices (GAP) certification is a third-party audit program under the USDA Agricultural Marketing Service. It covers farm food-safety practices: water quality, worker hygiene, pesticide handling, traceability, and harvest sanitation.
Many small farms don't pursue GAP certification because their primary buyers (farmers market customers, CSA members, independent chefs) don't require it. But once you want to sell to hotel groups, larger restaurant concepts, institutional buyers (schools, hospitals), or regional grocery chains, GAP certification is often required. Audits run several hundred to a few thousand dollars annually.