I sell used tires all the time. Not on Ebay but on CL. Good, high quality road tires with a lot of life left. GP4000's, Pro Race 4's, Gatorskins, Armadillos - many others. Cheap too. Like $20-25 a set depending on what else the person is buying. I give away good usable tires that aren't really worth selling. I once sold 76 tires to one guy...34 sets and a bunch of singles for $375. All of them were in good to excellent condition.