The following information is adapted from the Maine Attorney General's office:
The State of Maine has passed the Used Car Information Act that requires all car dealers to provide certain warranties and to post certain information on used cars offered for sale. As a buyer, if the dealer has not obeyed the law and refuses to repair your car, you may be able to force the dealer to take the car back and give you your money back. Further, if you go to court and win, the judge can also order the dealer to pay you liquidated damages of between $100 and $1,000 and your attorney's fees. In Maine, a used car is one that has been registered with the State. If a car has never been registered, then it is new. This is why some demonstrators can meet the definition of a "new" car. Please note: Motorcycles are not considered cars under this law.
However, if the dealer has fully complied with the Used Car Information Act, offered no express warranties (verbal or written) and has properly disclaimed any implied warranties, then the car need only to pass State inspection! If it can, and the dealer has not significantly misrepresented the condition of the car, the dealer is home free.
What this means is that for the above situation, if after several weeks of driving the engine fails, you may very well have no recourse against the dealer. An engine is not a State inspection item. Therefore, if you buy a used car "as is," your only warranty is that it can pass State inspection.
However, there are several other types of laws that can be used to help you in the event you discover that you've bought a used car lemon. First, the Federal Trade Commission (FTC) has what's called the Used Car Rule that requires dealers to provide consumers with a Buyer's Guide with warranty and other types of information. If the dealer has in any way failed to abide by the FTC Used Car Rule, you may have the basis for a legal claim.
Second, each state has what are called Unfair and Deceptive Acts and Practices (UDAP) laws. If the dealer has, for example, made verbal promises or didn't tell you about issues relating to your used car, you may have a cause of action. Third, Maine's version of the Uniform Commercial Code may provide you with relief. Finally, the Truth in Lending Act and the Federal Odometer Act might also be valuable in obtaining lemon justice.