I'm sorry but sometimes you've got to lie to them.

If they have something like gold-plated silverware or jewelry you can be more honest. You've still got to lie and tell them it sold for slightly more than it really sold for (they will bitch and moan anyway, wanting a super inflated price, but still), and give them a cut of what you got for it.

But if it's something stupid like furniture nobody wants, or figurines, for dishware, you've got to lie to their faces and tell them you needed the money for credit card debt. That is the only way they're going to stop tripping over their hoarded stuff and getting rescued by the fire department. "Please grandma give me this massive hoard of plates you have packed in cardboard in boxes all over the floor, I need it to pay off my non existent credit cards" and then throw that shit in the trash.