Although most states recognize and enforce oral contracts, the safest practice is to put any substantial agreement in writing. Get any promise from a salesperson or an agent in writing, especially if there already is a written document that might arguably be a contract covering any part of the same deal. Anything not in that written contract would be deemed not to be part of the deal. This requirement, which exists in varying forms in nearly all the states, had its origins in the famous statute of frauds, an English law dating from 1677. In most states, the courts will enforce certain contracts only if they are in writing and are signed by the parties who are going to be obligated to fulfill them.
Some states have additional requirements for written contracts.
These statutes are designed to prevent fraudulent claims in areas where it is uniquely difficult to prove that oral contracts have been made, or where important policies are at stake, such as the dependability of real estate ownership rights. Promises to extend credit are often in this category. If they aren't, and the repair is done anyway, the contract may not be enforceable, and the repair shop may not be able to get its money if the customer disputes authorizing the repairs. A signature can be handwritten, but a stamped, photocopied, or engraved signature is often valid as well, as are signatures written by electronic pens. Even a simple mark or other indication of a name may be enough.