Mr. Deepak is a cautious consumer. He had taken the cash memo for the book he purchased. Therefore, he can recover the extra money (Rs.20). Besides, as per the Consumer Protection Act, 1986, following option are also available to him against the book-seller:
(i) He can return the book and ask for the repayment of Rs.200 which he paid for buying the book.
(ii) He can sue the book-seller for using unfair trade practices.