I found Thred Up when I was researching a website that could pay me for my gently used clothing. Initially, I wanted to host a garage sale, but I live in an apartment complex and that would be too much trouble. Then I revisited ebay, but it appears that the sellers are required to pay taxes on their sales which is also too much trouble. My mission was to empty my closet and make a couple of dollars as well.
Then I found Thred Up which offers to pay contributors so long as they meet the checklist of acceptable items. This seems like the best route for my spring cleaning :)
Beware! They do not take just any old items. Visit their website to read about what items they will likely pay you for.