Hiring a tradesman

I need some advice regarding hiring tradesman. Just wondering when hiring a tradesman for work on house/unit that cost more than $2000, do we usually need to sign a contract to make sure what we get is equal or greater than what we expect from the tradesman? If there's no contract, how would people normally solve issue with regards on crappy work or unsatisfactory result?
Home Building Act!

Any home building work that is over $1000 including any labour and materials must have a contract and have a seven year warranty on workmanship.

Check the Dept of Fair trading website, has heaps of info that will be relevant..................

Big Tone