Thredup is a sham. Here is an example-
The following item is posted on thredup for $8.99 and the compare price is shown as $18
https://www.thredup.com/product/women-vassarette-black-tights/*******
However if you check ebay for the same product (brand new) it is available at $2 only.
http://www.ebay.com/itm/Vassarette-Her-Secret-Classic-Black-Stockings-Size-Medium-5-1-5-10-/*******078?hash=item25afcb1d5e:g:WD0AAOSw8d9Uu76N