Residential Tenancies Act 1986

The tenant shall be responsible for anything done or omitted to be done by any person (other than the landlord or any person acting on the landlord’s behalf or with the landlord’s authority) who is in the premises with the tenant’s permission if the act or omission would have constituted a breach of the tenancy agreement had it been the act or omission of the tenant.

Where any person (other than the landlord or any person acting on the landlord’s behalf or with the landlord’s authority) intentionally or carelessly damages the premises while the tenant is in the premises, it shall be presumed that the tenant permitted that person to be in the premises unless the tenant proves that he or she took all reasonable steps to prevent that person from entering the premises or (as the case may require) to eject that person from the premises.