ThredUp is "the largest online thrift and consignment store." While you can still find luxury goods on ThredUp, it's more so a place to buy and sell clothes and accessories from mid range big brand names, ranging from Ann Taylor, J Crew, to Michael Kors.
If you have heaps of used clothes to toss out, request for a "Clean Out Bag" to be mailed to you (free!), toss in your goodies when the bag arrives, drop it off at the post office, and sit back, wait, and watch your $$ come in as your accepted products sell.