No one can give you a menaingful answer without reviewing the exact language in the contract you signed and discussing the details of any fraud claim you may have.
Generally, if you breach a contract, the other party can sue you for damages and get a judgment against you.
Since you categorized this in NV, maybe NV law applies, and maybe you agree to resolving any disputes in NV court. If you didn't defend the suit, they'd win by default. Then they could take that NV court judgment and "domesticate" it, i.e. get it recognized, by an Australian court, and enforce it in AU. That of course would impact your credit in AU, and they could levy your bank accounts, garnish your wages, put a lien on your personal and real property, etc.
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There are generally two types of timeshare interests in Nevada. The typical timeshare consists of an interest in real property, but there are also timeshare interests which consist of a contract right to use the property. Either way a review of the ownership documents would be required to determine what recourse the seller or management company may have against you if you breach. Ideally you could resolve the breech without having the company seek damages here or in Australia. I have had success in assisting clients transfer timeshare interests back to the management company with minimal costs, but every situation is different. I would recommend that you retain a Nevada attorney to review the relevant documents and communicate with this company on your behalf.
Also, an attorney should be able to assist you in determining whether you have any recourse against the seller for fraud, misrepresentation, or failure to comply with the applicable state law.
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I just wrapped a cancellation of a timeshare here in Nevada for one of my clients and the company surely did not make it easy. I definitely agree with my colleagues above and think that you should have a lawyer take some time to review your contract. In my own personal experience with timeshares, it only established a very small ownership interest (ie: a right to use). That right had to be cancelled by selling the right to use back to the HOA because the market for timeshare resale is almost nonexistent. In essence, you will likely have to pay a small fee in order to "sell" your right to use timeshare back to the company that sold it to you.