One of the major underlying restrictions is the (commonly known as) Statute of Frauds[1]. State law can supersede it as it is Common Law inherited from England (and therefore "default" law in USA where something doesn't supersede it), but most states either follow it or have state laws that copy it. From the link, the specifics it covers, that are required to be non-verbal are:

* Any promises made in connection with marriage, including such gifts as an engagement ring.

* Contracts that cannot be completed in less than one year.

* Contracts for the sale of land—leases need not be covered unless they are for a year or more.

* Promises to pay an estate’s debt from the personal funds of the executor. However, promises to pay such debt from the estate's funds are not subject to the statute of frauds.

* Contracts for the sale of goods above a specific dollar amount, typically $500.

* A contract in which one person promises to pay the debt of another person is considered a surety and is subject to the statute of frauds.

So when I tongue in cheek reference a really bad car, I'm talking about a car whose value is under $500. :)

[1] https://www.investopedia.com/terms/s/statute-of-frauds.asp