Is this a GREAT deal or HUGE headache??

[Will B.]

In a tough situation and hope someone has some insight on this..Met with a highly motivated seller in a completely trashed house, regardless, it has great potential for a rehab and will make a BIG profit once we agree to a price.
HERES the issue. The guys mother-in-law Quit Claim Deeded the property to him because she was in some type of financial trouble and didnt want to lose the house (free and clear). He is trying to sell it, without her knowledge, but remember HE legally owes the house, she is STILL living in the home... Now with her in the house not paying anything but also NOT being the legal owner what can I do? I KNOW that she wont take cash for keys, She sat there and told me she put 300K in the house while blazing up a cigarette in the filthiest kitchen Ive ever seen with broken tile and paint chipping everywhere, Actually quite an ironic moment. Anyone have an idea of how we can get through this with out a HUGE hassle? Or is this just a deal I should move on from? Not looking for a lesson in morals here, The woman has had several instances with the law involving drugs and other things so not exactly an upstanding citizen. Just getting that out of the way. Thanks in advance for any insight here!