...the art of showing someone exactly how it is in their best interest to do what you want them to do.
The way I got the owner of the property with the neighbor from hell (NFH) to give me power of attorney to get rid of her, was that I showed him his liability for keeping her there, and then made him an offer he couldn't refuse to let me do it for him.
The way I got rid of the NFH was to have the attorney tell her that if I even filed a suit for unlawful detainer (the technical term for eviction lawsuit), it would be follow her around for the rest of her life, regardless of the disposition of the suit. It's amazing how fast people can move when they're motivated!
The way I'm hoping to convice the lender to sell to me cheaply is to point out that if they don't, they become liable for the myriad problems on the property, and that the Homeowners' Association can foreclose judicially at any time, which would wipe out their interest entirely. Wish me luck!