ThredUp will buy your clothes (especially designer but also mall brands) & give you cash or store credit. They also buy brand name kids' clothes. I discovered them about a year ago, & I've earned enough from selling my castoffs to them to buy a couple things. I've also earned a small amount of cash.
The clothes I've bought have all arrived quickly & in perfect condition in a fun green polka-dot box or bag. Selling clothes has been easy & has included free shipping.