Written agreements are definitely much better than verbal agreement. As most of the participants mentioned here, that written agreements are easier to defend in court because you have a document that is legally binding which is easier to use in court if things went awry. This is also the main reason why documentation is stressed a lot not just in school but in everyday life. A simple example is a receipt which is a proof of purchase where items and prices are listed as well as return and exchange policies are clearly written to protect the merchants and customers if the product is abused and was tried to be returned or if the product is defective and needs to be replaced, respectively.