The last time I moved house, I paid a removalist to get rid of a bunch of my stuff. Paid them by volume of removed material; they did all the work to take the stuff away. (I basically said "take everything in that room over there"). Took a couple hours, and it was done.
They disposed of everything responsibly, and would try to sell things which were reusable or salvageable. The cost to me was dead cheap, because most of their profit (I assume) came from reselling the stuff that could be salvaged.
It's too bad because that seemed like a reasonable system: people would get to be proficient at pricing, describing and listing items on eBay and the sales price at a public auction seemed like a pretty accurate value for what something was "really worth".
My wife used to take things that our kids outgrew to resale shops. She still is able to take some things that we no longer use but was easier with kid stuff.
Mostly I just donate things these days to the Salvation Army or whatever. Unfortunately, not everything is really amenable to that. I have some items that I'm sure are worth something to someone but they're not worth my effort to sell on ebay and Craigslist is pretty thin out where I live.
You'd get a load of garbage that people are too lazy to sell on Ebay, and too sentimental to throw out.
I don't tend to keep useless things around as it is. I imagine there are quite a few people like that. I imagine at least in some strata of tech workers, who are into the latest and greatest, there are quite a few who'd have pretty decent things to recycle.
I've worked with people who just have too much disposable income as either singles or DINKs and buy/consume "accordingly."