(VLR) During the implementation of the contract, the parties may agree to change the terms of the contract but do not know whether it is necessary to make an annex to the contract or not. Enterprises can render service to each other but do not know whether it is a contractual obligation or just an assistance. When collecting a debt, may it be different from the contractual provisions on kinds and contents of documents or not. Failing to study carefully the Standard Trading Conditions of logistics businesses (specified clearly on the documents of the transaction) may result in the adverse outcome during the implementation of the contract.