I agree with everyone: seller should disclose everything. But, anyone that's been in the hobby for any length of time knows that there are quite a few folks out there that will lie about and gloss over issues. I've been screwed twice... once by someone who actively sells on this site all the time. In fact, the crap this guy pulled happened to him (with the same machine when he bought it), and I later found a thread on Pinside where he was explicitly bitching about the undisclosed issues he found when he bought the game! No joke.
In hindsight, the real issue is my willingness to accept someone's word without 100% verification. Sucks to say that, but once you get screwed a few times, it becomes really obvious that – as a buyer – it's your responsibility to completely check over a game before you hand over cash.