If you're even vaguely Christian, you might want to consider getting the house blessed. (Of course, that tends to just piss demonic entities off, but hey, if blood doesn't start dripping out of the taps, at least you know it's just a ghost. It may even help.)
I also think that, at least in some jurisdictions, an undisclosed death in a house may be grounds for legal action (although I'm not sure, and it may only apply to a violent death or a suicide.) I also seem to recall a successful lawsuit regarding a known haunting not mentioned at the time of sale.