The most common type of implied warranty is the warranty of merchantability, which means simply that the seller promises that the product offered for sale will do what it is supposed to. That a car will run is an example of a warranty of merchantability. This promise applies to the basic functions of a car. It does not cover everything that could go wrong. For example, breakdowns and other problems after the sale don't prove the seller breached the warranty of merchantability. A breach occurs only if the buyer can prove that a defect existed at the time of sale. A problem that occurs after the sale may be the result of a defect that existed at the time of sale or not. As a result, a dealer's liability is judged case-by-case.