For the past three weeks hundreds of Australian Defence Force personnel have been helping thousands of people with the herculean clean-up from last month's catastrophic floods across NSW.

But the troops are withdrawing and affected communities will have to hire help to repair their properties.

NSW Fair Trading Commissioner Rose Webb warned scammers often took advantage of vulnerable people after natural disasters.

"Consumers are reminded that anyone who undertakes work to rebuild or repair damaged homes is required to have a valid licence," Ms Webb said on Wednesday.

Home owners should avoid workers who showed up uninvited offering their services and should also check with their insurance provider before authorising repairs.

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"Consumers should avoid cash transactions if possible as credit card payments are a better option as charge backs from banks may be available.

"It's also a good idea to ask family and friends for a recommendation rather than choosing a trader from an advertisement."

Previously unlicensed tradies have targeted affected communities offering house repairs, concreting, paving, structural landscaping and roof repairs amongst other services.

Those services require a licence if the work is valued at more than $5000.

Fair Trading offers an online tool on its website where consumers can verify licence details and check whether a contractor or tradesperson is qualified to do the job.

When choosing a tradesperson or contractor, NSW Fair Trading advises consumers:

* Get two or more written quotes

* Don't hand over money before meeting your tradie.

* Ask for references and examples of past work

* Avoid payments without a written contract

* Avoid paying significant deposits

* Anyone who has problems with tradies can lodge a complaint online

Australian Associated Press