Brian was moving to Cairns, so appointed 'Thunder & Antlers, Real Estate' to manage his house in Sydney. He discussed with them the weekly rent he desired, $600, and that no pets were to be allowed. He then authorized them to sign the appropriate lease documents on his behalf. Mr Lightning, a member of the real estate firm, found, after 3 months, a family willing to rent the property but who only offered $550 per week rent. He tried to contact Brian but was unable. As the house had been vacant for some time, he got back to the family and said "Yes, $550 is fine." The lease was drawn up but Mr. Lightning innocently omitted reference to no pets as he had not read Brian's full written instructions. The family moved in with 3 cats and 2 pet rats. Has the agent acted with authority?

Discuss.

Further does Brian have any action against Thunder and Antlers? Explain your answer referring to relevant law.