If the salesman signs without the customer's consent, the contract would not be valid or enforceable against them.If the customer incurred any costs or liabilities due to the salesman signing the contract, the customer could sue both the salesman and your company (which, if it is a sole proprietorship, means the owner personally) for such losses or costs.A salesman signing without consent is commiting a crime--e.g. fraud or identity theft--and could face prosecution.The way to protect yourselves is to not let the salesman sign contracts for customers.