In this country it is mostly self-regulating. The certifying agencies set the standards and most certifications are accepted everywhere. For example, a PADI open water cert is recognized by other agencies as equivalent to their own open water cert.
You can buy most any kind of gear without any certification, but you cannot get air fills, get on a dive boat, or into operations like dive quarries without a c-card. To obtain more advanced stuff, such as nitrox, you need the appropriate certification.
Potential liability keeps things in order. Thankfully, this is one area the government has let pretty much alone (so far).
