Most of my old stuff I trash. One of my sisters had an absolute fit, pulling stuff out of my trash and exclaiming I could sell it. Sure, I could - for a little bit of money, meaning it wasn't worth my time. And the thrift/donation stores get rid of up to 90% of the stuff donated to them, mainly because they simply haven't got enough room for all of it. So I figure I'm saving them the trouble and expense of trashing my marginal-value stuff.
If I think they can sell it, and for enough to make it worth their trouble, I'll donate it, or give it away to anyone who wants it.
I got talked into putting some stuff into my sister's garage sale this past weekend. She then shanghaied me into helping her set it up, work it, and clean up afterwards. I probably made two bucks an hour after all that time. It was a complete waste of a beautiful weekend. Never again.