Dave is negotiating with Elsie for a second-hand Mini Cooper Countryman she has advertised for sale. Elsie advertised the car for $30,000. Dave inspected the car and offered by telephone to buy it for $25,000. Elsie replied that $25,000 was too low and said anything below $28,000 was non-negotiable. Dave contended that the price was too high and asked for more time to consider.

Thirty minutes later he phoned Elsie saying that he had changed his mind and agreed to pay $28,000. However, Elsie replied that the price was reverted to $30,000.

Advise both Dave and Elsie of their legal position. (500 words)

Pls provide the answer based on the australian legal system