Would you ever buy a house if you could get a really good deal on it, and it was right next to a lovely park and a trail, but a murder-suicide happened in it? (And it was cleaned and repaired)

Absolutely! I don't believe in ghosts, I like getting good deals, and I'm not afraid of being known as that person who lives in a haunted house. My only concern would be if it had been truly deep-cleaned, because I would be unhappy to find traces of blood or whatever a few years down the road.