it all depends.
For big dealers, such as Toyota dealer (they sell used cars too), you may not need to.
For small used car dealers, they are even better at cheating than individual sellers, you'd better check out the cars carefully, either by a paid inspector, or your friend who really knows cars.
For the used car dealers owned by the middle east people (there are many here in our city), don't do any business with them. No matter how careful and smart you are, they are smarter than you.