I was buying a pinball in Florida last year and the guy had an original Pacman in very good condition, and only wanted $350 for it, so better believe I made room on my truck for it too. I regret selling it, I had put a good monitor in it and a nice board and I offered it up here for I think $700 and it was scooped.
I'm actually buying a Pacman project for $150 just to make another because I love the game.
When deals come up, you have to be ready on the spot to drop everything and make it happen. There's a fine line too, depending on what the game is and the price, whether or not you're brave enough to screw around for a lower price or just tell them you'll take it and you're ready. One is the sure thing in your truck, the other is always a gamble that rarely pays off.