Do you have to promote individual cars? Or do you have to promote your friends car dealership as a whole?
If its individual cars that you have to sell - don't focus on what type of ads to run. Focus on where to run the ads. College campuses. Best place to buy and sell 2nd hand cars. Goes back to Gordon's
parade of life concept. Most likely point in life when people buy a 2nd hand car is when in college.