How would you explain this to someone and also using the cases

I. John instructs Ken to sell his car and signs a written contract to this effect. Ken operates a car mart. John then withdraws Ken's authority but Ken goes ahead and sells the car to Bertie. Ken has also told Bertie that he has authority from John to sell his 2 bedroom apartment for $2,000,000.00. Bertie gives him a deposit of $200,000.00. John has returned for his car to see Bertie driving it out of the Car Mart. He immediately jumps in front of the car and prevents Bertie from leaving with same. Bertie also tells him that he is purchasing his apartment and has paid a deposit for same to Ken. Advise John of his liability to Bertie for both the car and the apartment