A more thorough explanation:

Term: ex empto
Definition: Ex empto is a legal term that means something is based on a purchase. It comes from ancient Roman and civil law.
Examples: A warranty on a car is ex empto because it is based on the purchase of the car. Similarly, a contract for the sale of a house is ex empto because it is founded on the purchase of the property.
Explanation: Ex empto means that something is based on a purchase. The examples illustrate this because both the warranty on a car and the contract for the sale of a house are dependent on the purchase of the car or property. Without the purchase, these legal agreements would not exist.