I am amazed at the number of people who buy a camera,take some photographs, add photography after their name a think they are a photographer. It is owed to anyone using your services that you have some knowledge of the workings of a camera & related matter & you owe it to yourself to have some basic business acumen and legal knowledge relating to contract & photography laws.
I have come across so called photographers who do not ask for permission to take an obviously "private" photo. Neither have they known or bothered to find out about the legality of shooting at a park, event or zoo etc..
I also cringe when I see " I've got a wedding what sort of lens do I buy?" or "Do I need a back up camera for weddings?" If you are touting yourself as a professional be one.
If you are serious about calling yourself a photographer register as a business, take some courses & pay some taxes (or not as the case may be) the same as the rest of the profession. It does have benefits.
You must register for GST if:
1. You are carrying on an enterprise
2. You're annual turnover will exceed $75,000
Whether you register or not depends on advice from an accountant.