I just talk to the donator and find out what they expect and work it from there.
A coworker friend of mine's mother just passed away and her mom was a garment sewer and had tons of stuff to be gotten rid of. My coworker kept her Mom's machine but was getting rid of everything else and offered it to me. I took a look and told her honestly that as a quilter I had not a lot of use for her her mom's huge stash of bias tapes and knit fabrics, etc. but I would be willing to take it off her hands, pull what I wanted, and donate the rest on her behalf to a local fabric second-hand shop that benefits the local senior center. She didn't want to do that, she preferred have the stuff go to people she knows, so I helped her figure out what she had and who else at work was a sewer and almost everything was claimed that way instead.
I felt good about that!
Another garment-sewing coworker was moving out of the country and had a modest stash - she was perfectly happy to let me take everything, keep what I wanted and donate the rest. She regarded me taking it all as a favor - one less thing for her to hassle with. (I ended up keeping most of
her stash - it was pretty small and she had a lot of good quilting cottons that suited my style.)