While cleaning up his parents' storeroom, Joe found an old Spiderman comic book that belongs to his grandfather. He knows that collectors are willing to pay high prices for an old and rare edition of such comics. Joe cleans the comic, takes pictures of it, and posts them online, putting a price of RM300 for the comic. Bob contacted Joe saying that he is willing to buy the comic for RM300. Bob made the payment and on the appointed date, Joe handed the comic over to Bob.

Two days later, Joe contacted Bob saying that their contract is void due to a mistake. It turns out that the comic is worth much more since only a few copies are available. A check on the Vintage Comic website shows that the price can run up to RM2000. So, Joe wants his comic back and is willing to give the RM300 back to Bob. However, Bob disagrees and says that their contract is valid, and he is keeping the comic.

Advise Joe on the validity of the contract based on the rule of mistake and whether he can get the comic back.

(6 Marks)