FB groups with ppl in your local area is the way to go. When I revamped my equipment and wanted to start from scratch... I sold all but 3 balls out of 22 that was for sale in my local area including outside the city. The other 5 balls went to Chicago, Washington, Arizona, and Florida... I'm in California.
I had set a return value for each ball and was stiff. Minimum I made was $15 up to $60. Just like selling a used car, if the head light lens are crystal clear, it can increase the value of your car. So with the balls I sold, I cleaned it - dull or polished and kept original boxes for most.