Just like commercial contracts, the validity of family law agreements can be challenged under the law of contracts. Someone challenging an agreement can argue that:
#*they were under some sort of ''duress'' or ''coercion'' when they negotiated or signed the agreement, and didn't enter into the agreement voluntarily, of their own free will,#*the agreement is ''unconscionable'' — in other words, the agreement is obviously and seriously unfair to a party with no reason for that level of unfairness,#*they signed the agreement without having independent legal advice and didn't fully understand what the agreement meant, and, as a result, they signed it by ''mistake'',#*the agreement was signed without ''full disclosure'' having been made, or#*they were tricked into signing the agreement because ''misleading information'' had been provided by the other party.
Arguments like these challenge the ''validity'' of an agreement.