I have no problem with people deciding they don't want to sell their house to someone else for any reason. I don't even care that this couple didn't want to sell their home to a black couple. It's a personal choice. I personally think it's a reprehensible reason, but I'm not going to tell people what they can and can't think.
But they shouldn't have accepted the offer, then refused to sign the papers. That does make them criminally liable.
39 minutes ago