I sent a bag to their J.Crew always program. In that case, you're supposed to send either items made by J.Crew or similar brands. The bag was packed full. I could barely get it shut, and it contained mainly dresses from J.Crew, Ann Taylor and Michael Kors. All were in good condition. I could've sold them on Poshmark and probably made $15-$20 each based on other sales I've done. But I thought, why not give Thred Up a go?
Oh my God, after waiting 3 to 4 months, I got an email the other day congratulating me on the $15 I made for the entire bag. I really wish I had not sent them my dresses. I feel so ripped off, and I think they are ripping off everyone who uses their site. As far as selling clothes. If you are in it just for the environmental/recycling reasons then I guess go for it. But you would probably be doing a better deed by donating to a Dress for Success program and not corporate greed.