I had only been in the hobby a couple months when I came across an Eight Ball Deluxe, the '84 "nice cowboy" version, on CL for 1600. It was nice but needed a thorough cleaning and shopping, and I talking the owner down to 1100. Came back the next day and like an idiot I hemmed and hawed and finally passed on it because what I now assume was just a sticky switch was racking up points without the ball hitting anything, but to my mind then this was a huge problem. Came to my senses later that week but it was already gone. Sounds a bit like pezpunk's story above.
And then just a few months ago there was the $700 Flash Gordon that Crispin clued me in on, with some sort of board issue. I passed like a dope, and he went it picked it up after all, and it was in much better condition than I had thought it would be. Duh.