One of our clients recently bought a single keyword domain for their new online (legit) business. I think the price they paid for it was in the mid xx,xxx range and they never bothered checking, or getting someone to check, its history.
Turned out over 14 years it had been abused by several porn, gamble and pharma affiliates. The domain wasn't indexed in Google. After a (detailed) reconsideration request, the site has been included again. My next steps will be using the disavow tool so when the time comes for another Penguin update, the site won't get penalized for past affiliations with spam sites.