In all the my years working in repair shops, I cannot count the amount of cars I've inspected that have exceeded the purchase price based on repairs needed — after the customer brought their 'new (used) car' in for the leak or noise they didn't notice when buying the car.
Unless you are a professional with the right equipment, there is no way to know if you are buying a lemon or not. I don't want to discourage anyone from buying a used car, I just strongly encourage you have it inspected before making a large investment.
Call me, and I will perform a thorough inspection of the car you are considering buying. I will travel to the car lot or vehicle location.