I recently moved from Seattle to the UK. Part of the process of doing a big move like that is getting rid of stuff that you don't need any more. For some things that's just a question of throwing it away (we had one visit from the haulers, two trips to the tip and several weeks of extra garbage charges). But there's other stuff that, while we didn't need it any more, would have some value to someone else. Getting rid of all that stuff was a consistent feature of all our todo lists, and we still didn't manage to get rid of as much stuff as we wanted. We gave some things away to friends, sold some things on a neighborhood email list and had a (not particularly successful) garage sale.
There really ought to be a better way than this. There must be a enormous amount of value locked up in peoples houses in the form of stuff that they don't use but which still has some value and therefore they don't want want to throw away, but getting rid of it is an annoying, difficult, low priority task, so never gets done.
I think somebody could make a fortune by setting up a company that takes away your unwanted stuff. You'd request a visit from them on their website (or maybe they could just show up on a regular basis) and take away anything that you didn't want. They'd do the work of valuing it, selling it and shipping it, and then send you the proceeds (after taking their cut). If, after the valuation stage, you decided that the item was worth more than that you could reject the offer and they'd bring it back with the next visit (perhaps for a small charge to avoid the service being abused as a free valuation service). Items that might leak liquids or emit odors would probably not be accepted (the small amount of value held in such items would probably not be worth the possible damage to other items).
They'd do all the work of making sure that items were packed sufficiently well for shipping, reusing packing materials as much as possible (and eliminating a large amount of waste). If they delivered items as well (instead of relying on UPS, Fedex or similar) they could take away the packing materials on delivery, helping the environment and saving the customer from another annoying job (my workshop in Seattle often used to get cluttered up with old cardboard boxes, packing peanuts and bubble wrap).
Another nice thing about this business is that it would be really easy to bootstrap - you could start it off in just one city with a couple of people, a van and a simple website and some insurance against breaking things. Deliveries to places too far away for the van to get to (or between two different cities where the company does have vans) could be done with the existing delivery services. After visiting one house for a requested pickup they could visit other nearby houses and ask if they have any items they want to get rid of.