Dealer:

The Federal Trade Commission’s Used Car Rule requires dealers to post a Buyers Guide in every used car they offer for sale.

The Buyers Guide gives a great deal of information, including: whether the vehicle is being sold "as is" or with a warranty; what percentage of the repair costs a dealer will pay under the warranty; the fact that spoken promises are difficult to enforce; and the major mechanical and electrical systems on the car, including some of the major problems you should look out for.

The Buyers Guide also tells you to: get all promises in writing; keep the Buyers Guide for reference after the sale; and ask to have the car inspected by an independent mechanic before the purchase.

Private Individual:

Buying a car from a private individual is different from buying from a dealer.

Private sales generally aren’t covered by the Used Car Rule, or by "implied warranties" of state law. You’ll have to pay for anything that goes wrong after the sale.