Jing, another of your clients, shares with you that his elderly parents who migrated from China recently and have little English language skills borrowed money from the Super Money Lenders Pty Ltd without his knowledge. Jing thinks that Super Money Lenders has charged an exceptionally high interest on the loan and some terms are very unfair. Jing wants to know if the loan contract be avoided.

Explain the most appropriate principle of contract law that Jing’s parents may rely on to challenge the validity of the loan contract? You are not expected to refer to any statutory law (legislation) in your answer.