If a client refuses to sign a contract with you, as a freelancer, you don't need to continue with such a task. This is because such a contract is not backed by any legal entity. Ensure that you don't fall for the cheap gimmicks of the clients. There are many of them that will tell you that you need to trust them. You don't listen to them. You should make sure you have your personal lawyers that will interpret some difficult aspects of the contracts.