This happens oh so often and never gets dealt with. I have a niece (on my wife's side of the family) that is on SSI Disability and "can't work" for "back problems". I took pictures and video of her running a roto-tiller in a quarter acre garden and submitted them to Social Security. I was told that they couldn't do anything about it since she was not "gainfully employed and receiving compensation".
Glad they busted this one, especially since I am a Postmaster and see these kinds of cases often enough that I know the system is being abused by some.