I don't have this issue at all since no one else in my family knows how to sew or quilt. They all honestly admit they have no idea what would be valuable to my quilting business if it came up & smacked them in the face.
I used to teach, though, I would get a ridiculous amount of books donated. Many of them I really loved getting because my students typically didn't own any books & were thrilled to get donations. Sometimes, though, I would simply have too, too many ... or the books would be WAY to advanced or too simple for my little guys to enjoy. So I would do one of two things: I donated what I could donate if finding a new home was easy enough. Then I would sell/swap the rest and contribute the proceeds to a worthy cause. That works great when relatives try to guilt you about getting rid of stuff ("oh, yeah, I didn't really have space for it, so someone gave me a good amount of money for it & I donated that money to Grandma's favorite charity in her memory"). Shuts them right up. lol.