What are the "normal" horror stories of buying a used car/handling car dealerships?

I'm from America, and my foreign (India) girlfriend is planning on shopping for a used car soon. She has no idea how badly car salesmen try to screw you over on repairs, sales, etc. etc. I don't want the worst-of-the-worst horror stories, but can you guys tell me some stories of run-of-the-mill car dealership occurrences that characterizes the overall experience?