No qualifications needed sadly. The only issue is the builder is responsible for a few issues, like builders plates, and build quality, but only along the lines of if there's ever an issue and the boat somehow is found to be faulty, then the builder would/could be liable.
It's a bit of a farce. In QLD a while back, as a joke and to show just how silly the system is, the QLDBIA registered a wheelie bin, and took it boating..
As for state to state, much of the management is moving under AMSA so trying to nationalize the industry some.
Out of interest though, anyone who imports a boat from overseas, is also responsible legally for that vessel, for the life of it, so again, if say someone imported a big brand name from somewhere and a huge flaw was later found, the importer would/could be held responsible also.
Hope that makes sense..