If a spirit willingly attaches itself to an earthly object, and if they willingly do things for that object's physical owner, that's their decision. I just have issues with the concept of forced servitude on any plane: earthly, astral, spiritual, etc. If we start taking part in that, we're ensuring that we will have an awful lot of things to answer for once this life is through. And from where I sit, even if the "enslaved spirit" is nothing but a fable, the purchaser's INTENT to enslave a spirit wasn't a fable, and that's going to cause some big karmic issues down the line for whoever gets involved with these haunted items. It's another caveat emptor situation.