First off, if you're buying from ThredUp, it's a complete crapshoot of what you'll end up with in the mail since they provide NO measurements and don't give any real details about the TRUE sizing. For example, I got a FREE PEOPLE tank marked L and it fit like a S. You CANNOT go by their pictures.
Another time, I bought a pair of Prairie Underground pants and was so excited. I waited and waited and waited and finally contacted them. Was told abruptly that they ;d "be there soon." They finally arrived a month later without explanation or any credit for the hassle.
Then, sending it back is a pain as you have to pay for return shipping.
As for SELLING, ThredUp is horrible. Notice on their website they don't specify where their unaccepted clothing goes. I sent in a HUGE bag chock full of stuff and got $9. I made sure it wasn't from Target or Old Navy and all that-- it was JCrew, Hanna Andersson, etc.
When I sent my first bag when the company was a fledgling site, I got $60 for my bag. Clearly this company has learned the art of ripping people off to their benefit.