Did you know that the BSA law states that any person supplying a quote or offering to build a wall is required to hold a current BSA Contractors Licence and a Gold Card, and this number must be stated in there advertisment or web page. It is against the law not to advertise this number. If they are unlicenced,they must state this in there advertisment and state that they can only do non structial works to the value of $3300.00. Ask them to show you there licence or show them the gate. They must give you a writen quote, then a written contract with a householders imformation booklet stating your rights and giving you a 5 working day cooling off period before they start.

Even if the wall is only .300mm high, If it is retaining soil, it is a retaining wall and you are not covered by insurance, and they are breaking the law. Any wall built over 1 metre in height must be inspected by an Engineer and the Contractor must supply you with an Engineers Certificate, How can an Engineer certify an unlicenced Contractor? I have repaired or rebuilt many walls for Householders who have tried to save a thousand dollars by using a cheaper quote from an unlicenced Contractor and have had to refinance to repair the damage. You can check Contractors out on the BSA site under Licence Search and type in there name. Mad if you dont. Why would you risk it.