If you can be calm enough - or maybe even your kids might pick up on it - just need to ask said ghost what it needs or wants or why he's there. Maybe he will be a protector to your family... You never really know without asking.

And there is no certainty that the RE agent has any clue about it anyway. Could be just a complete fabrication.

I am sure many others here will have more advice - but don't panic hunni, its not a bad sign for your house purchase.