Under Queensland law, all building work over that has a total value of $3300 (inc GST) or more must be carried out by a licensed contractor.
The $3300 includes the total cost of all materials and labour to complete the job (not just parts of it). Visit this link to find out more.
If in doubt, simply ask them to show you their QBCC Act Licence or search online.
Your property is a huge investment, can you afford NOT to use a qualified and insured individual?