I’m 67, and until recently, I lived with my daughter, Sarah, and her husband, Mark, while they saved for a house. I didn’t mind the arrangement; I loved the company, and I was happy to help them get a head start. However, I always had a gut feeling about Mark. He had a way of looking at things—not with appreciation, but with an eye for their price tag. He always seemed a bit sneaky, hovering just on the edge of too-friendly.