Because there are some used auto dealers that are most likely good in deception, they will do anything possible to sell the used car as high price as possible. Some auto dealers also use some tricks such as having to roll back the odometer just to give the used car a high value price. But not all used auto dealers are engage in such kind of work there are also good dealers that is honest and run a legitimate business which do not practice this kind of deception and fraud tactics.
However, if you want to buy a used car you must be aware of the behind the scene that sometimes does by a used auto dealers.
Therefore it would be better to look first for a private party selling their used car before going into dealers to avoid some fraudulent tactics that most used auto dealers are up to.