I loved that site when it first came out several years ago, but like another person's experience that was shared here, I also had things 'rejected' and then resold, and I decided not to use them anymore. I was pretty upset because I knew exactly what went into the bag, but I couldn't prove anything (and I had chosen not to receive any rejected items back because I had trusted them). I had a lot of name brand items in perfect condition and they were not accepted, but I saw them being sold later on, so it's not like I'm just out of touch with reality and overvaluing my own items or anything.
Also, I understand that they receive a great volume of items, so the return on two giant bags of great clothing isn't much. It's like 10-20 dollars, if even that. I have much better luck re-selling items on Poshmark, or if it's a luxury brand, then The Real Real. Although re-selling yourself takes more time, at least you know some company isn't technically stealing your items. As a buyer on Thredup, I didn't like that they switched their policy to store credit and a lot of times items were misrepresented (had received some items that obviously had a rip, etc.) when it said it was 'like new.' So I don't recommend Thredup at all. They really have no incentive to do a better job because everyone keeps throwing clothes at them.
For buying, I also like Poshmark, or the local thrift stores, which actually have great stuff.