The discount represents most possibly a "Fantastic deal" .
Explanation:
In the given advertisement the car is sold at a price that is 20 percent lower than the average selling price of a brand new car with the same options such as it is "fully loaded", 6 months old and had been driven 5,000 miles.
This is said to be a conditional phrase initiated by the seller, and it is acceptable as the offer seems to be an excellent deal or a fantastic deal for any person who is willing to buy a second-hand car in a good condition i.e, selling a car as in ('as is' refers to selling the car with all the known and unknown issues)