Regretted selling my SE-R, but couldn't justify keeping it as a "winterbeater" after I bought the Miata. It was still worth something (which, for those unfamiliar with the concept of a "winterbeater", automatically disqualifies it) and was stupid expensive to insure. I regretted selling it because I was 99% sure the kid who bought it would kill it. Sure enough, 6 months later, he learned about the magical attraction between poorly driven rice rockets and oak trees. Fortunately, the only thing dead was the car, but still. I knew before I handed him the keys how it would end. 
Which brings up a related topic, ever refuse to sell a car to someone because you decided they just shouldn't have it?
