Can you return a used 8 year old car to the person you bought it from and get your money back if the mechanic found new problems?

Probably not since most used cars are bought in "as is" condition when purchased used. Their is a certain amount of wear expected on a used car and it is not unusual for things to spring up after purchase. Did you receive a warrenty? to guard against this you should always have the car examined by a mechanic before purchasing. It cost around $50 - $100 and it will save you allot of grief in the long run.