About 15 years ago, my wife saw a "for sale" sign on a metallic blue '65 Mustang coup, my favorite color, vintage, and model. I called the guy and set up a time to check it out. It was beautiful. I took it for a test drive and when I got to a stop light, the engine started running rough. The owner (in the passenger seat) reached for the shifter, put it into neutral, and told me to rev it up. "It's the only way to keep it running while idling," he said. Then he told me that he'd brought it to four different mechanics and nobody could figure out what was wrong with it.
It was a damn fine-looking car, but I passed on it. I'm glad I did - it would have been a money pit.