Missouri's Lemon Law does not cover used vehicles, except in cases where the vehicle is a demonstrator or a lease-purchase, and has not been previously registered or titled. In those cases, Missouri's new car Lemon Law applies.
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, Missouri'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.