Can I get my deposit back if the real estate agent lied about the land's zoning?

In your situation, the real estate agent's actions appear to violate the protections provided by the Competition and Consumer Act 2010. Specifically, the law prohibits certain behaviors during the sale of land. Under the law, a person must not "make a false or misleading representation concerning... the use to which the land is capable of being put or may lawfully be put" [cite:au-competition-consumer-2010-sch2-sec30]. This means that if an agent tells you that you can build a multi-unit complex on a block of land, but the legal zoning only allows for agriculture, they have made a false representation regarding the lawful use of that land. Because the agent explicitly told you the land was for residential development and even put this in a printed brochure on 12 August, this constitutes a specific claim about the land's characteristics and use. This is a serious matter because the law states that a person commits an offence if they, in trade or commerce, make a false or misleading representation concerning "the characteristics of the land; or... the use to which the land is capable of being put or may lawfully be put" [cite:au-competition-consumer-2010-sch2-sec152]. The agent's claim that the contract was 'as is' and that you should have performed your own due diligence does not necessarily override these consumer protections. While buyers are expected to be careful, the law prevents sellers and agents from actively providing false information to induce a sale. However, the law provided does not explicitly state the specific process for a buyer to automatically rescind (cancel) a contract and get a deposit back; it focuses on the fact that the agent's conduct is an offence and a breach of consumer law. Whether you can successfully cancel the contract depends on how the specific terms of your signed contract on 25 August interact with these statutory breaches.