In this example, we learn that the contract specifies that the only way in which this can be modified is through writing. However, it is important to be aware of the fact that any such clause in a contract provided by a merchant to a non-merchant would necessarily have to be accompanied by a separate signature by the non-merchant in order to be effective. As this was not the case in the example, then the clause would not be considered valid, and the oral agreement could still be enforceable.
