private party car purchase

What is the name of your state? oklahoma
i recently bought a vehicle from a private party and the car was misrepresented. the car is a 2002 nissan altima 2.5s. and on the ad it says it a 6 cylinder but it's not it's a 4. not being mechanically inclined i accepted the posting. also the car engine started knocking the evening that i had just payed cash for the vehicle. can anything be done.

did you have an opportunity to look at and drive the car? did you have the opportunity to get it looked at by a professional and chose not to?

i did drive it and everything was fine. i did not have it inspected by professional cuz i took his word on the records shown by the nissan dealership.